The 3 Things That Can Make Or Break A Long-Term Relationship, According To Psychology

A relationship can have love, history, attraction and years of shared memories, yet still slowly begin to fall apart. That is one of the hardest things for people to understand when a relationship starts changing. Two people can genuinely care about each other and still discover that something important has weakened between them. Instead of knowing exactly what went wrong, they are often left searching through attachment styles, love languages and endless relationship advice trying to put a name to the problem.

More than four decades ago, psychologist Robert Sternberg proposed a surprisingly simple way to understand what happens inside romantic relationships. His theory says love is made up of three core ingredients: intimacy, passion and commitment. The balance between those three elements can change over time, and when one becomes weaker, a relationship can feel completely different even when the feelings between two people have not disappeared.

Robert Sternberg Turned Love Into A Triangle

In 1986, Yale psychologist Robert Sternberg published a theory arguing that love is not a single emotion that simply exists in greater or lesser amounts. Instead, he proposed that love contains three separate components that can each be strong, weak or missing. Those components are intimacy, passion, and decision or commitment, and the combination of those three elements can create very different forms of romantic love.

Sternberg described intimacy as the feelings of “closeness, connectedness, and bondedness” experienced in loving relationships. Passion covers the drives associated with romance, physical attraction and sexual desire, while commitment involves both the decision to love someone and the choice to maintain that relationship. When the three components are combined in different ways, Sternberg’s theory produces eight different forms of love, ranging from non-love, where none of the components are present, to consummate love, where all three are present.

That distinction is important because the theory does not suggest every relationship should look identical. One couple might have an extremely strong emotional connection but relatively little passion, while another might experience intense attraction without having much long-term commitment. A third couple could have deep commitment and intimacy even while their romantic excitement has changed dramatically since the beginning of their relationship.

Intimacy Is The Part That Makes People Feel Known

Intimacy can sound less exciting than passion, but it covers far more than affection or spending time together. It is the feeling that another person genuinely knows you, understands your vulnerabilities and remains emotionally connected to you when life becomes difficult. That can include trust, friendship, communication, caring and the sense that you can be honest without constantly worrying about how the other person will react.

Sternberg has described intimacy as including “friendship, caring, trust, and communication, too.” In everyday life, that means intimacy often appears through things that seem almost too ordinary to count as romance. It can be remembering something your partner mentioned months earlier, knowing how they behave when they are under pressure, understanding what kind of support they actually want or simply being available when they have had a terrible day.

The strongest examples of intimacy are rarely dramatic. They are built through hundreds of small interactions that tell someone they are being seen and understood. Bringing food home because you know they have had a difficult day, checking whether they arrived safely, remembering an important appointment or listening to the same problem for the tenth time can all reinforce that emotional connection.

That is also why intimacy can disappear without either person immediately noticing. A couple may still live together, share meals and spend weekends in the same place while gradually becoming less emotionally involved in each other’s lives. When that happens, the relationship can remain intact on the surface while one of its most important components is quietly weakening underneath.

Passion Changes, But That Does Not Mean Love Is Gone

Passion is usually the component people notice first when something changes because it can feel so different from the early stages of a relationship. New relationships often come with excitement, physical attraction and an intense sense that the other person occupies almost every thought. Years later, that same intensity may become less obvious, which can leave people wondering whether something has gone seriously wrong.

Sternberg’s definition of passion is also broader than sex. He has described it as the feeling that you cannot live without someone and the sense that a particular person has become deeply connected to your happiness. Sexual attraction can certainly be part of that experience, but passion can also involve romance, excitement, emotional intensity and the psychological pull that draws two people toward each other.

Research examining Sternberg’s theory has found that the three components can change depending on how long people have been together. Passion is particularly likely to shift as relationships move beyond their early stages, when novelty and constant anticipation naturally give way to familiarity and shared routines. A change in intensity therefore does not automatically mean that the relationship has stopped working.

What matters is the broader pattern. A relationship can experience periods when passion becomes less prominent while intimacy and commitment remain strong, and those elements can create a different kind of closeness. The mistake is assuming that love must always feel exactly as it did during the first few months for the relationship to remain meaningful.

Commitment Becomes Visible When Life Gets Difficult

Commitment can sound like the least romantic part of the triangle until a relationship enters a genuinely difficult period. When everything is going well, attraction and emotional closeness can carry much of the relationship. When life becomes stressful, however, commitment can determine whether both people continue investing in the relationship even when being together feels harder than usual.

Sternberg divided commitment into two connected ideas: the decision to love someone and the commitment to maintain that love over time. He has said this component “can be essential for getting through hard times and for returning to better ones.” That distinction matters because feeling love and actively choosing to remain invested are not necessarily the same experience, especially when a couple is dealing with financial pressure, family problems, health issues or major changes in their lives.

A 1992 study involving 204 adults tested predictions from Sternberg’s theory and found that commitment emerged as the strongest and most consistent predictor of relationship satisfaction, particularly among people in longer relationships. The researchers offered mixed support for the theory as a whole, so the result should not be treated as proof that commitment alone determines whether a relationship succeeds. It does, however, show why the quietest side of the triangle can become especially important when the exciting parts of a relationship are under pressure.

Long relationships inevitably contain boring periods, stressful periods and moments when one person temporarily has more to give than the other. Commitment can help provide stability during those periods while intimacy and passion fluctuate. It does not guarantee that a relationship will last, but it explains why some couples can move through difficult stretches without interpreting every low point as the end.

The Theory Was Tested Across 25 Countries

An obvious question follows from a theory developed by an American psychologist in the 1980s: does it actually apply beyond the culture where it was created? A psychological model can appear convincing in one population and look very different when researchers examine people from other cultures, languages and social backgrounds. Researchers therefore tested whether Sternberg’s three components continued to make sense across a much wider group of people.

A large cross-cultural study screened more than 11,000 respondents and conducted its final analysis on 7,332 people across 25 countries. The research included participants from every inhabited continent and examined whether Sternberg’s three-factor structure survived across different cultural settings and translations. The results supported the three-component structure at every level of invariance tested.

The evidence did not stop there. A later validation of a shortened 15-item version of Sternberg’s scale examined 60,311 people across 37 languages, again spanning every continent, and once again found support for the three components and their cross-cultural fit. That is significant because it suggests intimacy, passion and commitment are not simply three concepts that happened to fit one particular group of American couples.

None of that means every culture defines a successful relationship in exactly the same way. It does show that researchers have repeatedly found value in using these three components to describe romantic relationships across very different populations. For a theory that began in 1986, the fact that the same basic structure continues to appear in large international studies gives it considerably more weight than a simple relationship trend circulating online.

The Research Has One Major Limitation

There is an important limitation in the evidence, and it changes how confidently the theory should be used. A 2026 scoping review examined empirical research applying Sternberg’s theory to couples and identified 27 studies that met its criteria. The review found that the theory remained theoretically coherent and that all three components were consistently associated with relationship satisfaction, relationship seriousness and sexual satisfaction.

That sounds encouraging, but there is a major problem with drawing stronger conclusions from those findings. Every one of the 27 studies used a cross-sectional design, meaning researchers collected information at a particular point in time rather than following the same couples forward over several years. Researchers can identify relationships between intimacy, passion, commitment and satisfaction from that kind of data, but they cannot establish that increasing one component will necessarily stop a relationship from ending.

The review also found that evidence concerning relationship length and sexual orientation was mixed and inconclusive. That matters because relationships change over time, and a snapshot of how a couple feels on one particular day cannot fully explain what caused that relationship to become stronger or weaker later.

So the most accurate way to view Sternberg’s theory is narrower than some relationship advice makes it sound. The three components provide a useful framework for describing love, and they consistently appear alongside measures of relationship satisfaction, but researchers have not established that simply increasing a weak component will automatically repair a struggling relationship.

Every Couple Has A Different Version Of The Triangle

Perhaps the most useful part of Sternberg’s theory is that it does not claim there is one perfect relationship formula. Sternberg has said, “Each person’s ideal is different. There is no one ideal that works for everyone.” That means one couple might place enormous value on emotional closeness and stability, while another might place greater importance on passion and romantic intensity.

Problems can appear when two people quietly expect different things from the same relationship. One person might think commitment means lifelong monogamy, while another might define commitment differently. Both people can genuinely care about each other and still have completely different expectations about what their relationship should look like.

That difference can become particularly painful because neither person necessarily feels dishonest. They may both believe they are giving the relationship what it needs, while their definitions of intimacy, passion or commitment are simply out of alignment. A certified sex therapist and Sexual Health Alliance executive Heather McPherson has described commitment as becoming stronger when it is explicit rather than assumed.

That idea gives the triangle a practical purpose. Instead of asking whether two people love each other enough, couples can ask what they actually mean by love and commitment. The answers may reveal that the relationship has a problem that neither person had previously known how to describe.

The Three Parts Give Couples Something To Talk About

The triangle becomes most useful when it is treated as a conversation tool rather than a scorecard. Instead of deciding that a relationship is either healthy or unhealthy, couples can look at what is actually happening between them and identify which parts feel strong, which feel weaker and whether both people want the same things from the relationship.

There are three simple questions hiding inside Sternberg’s theory:

• Intimacy: Do both people feel known, trusted and emotionally connected?
• Passion: Is there still romantic, physical or emotional excitement between them?
• Commitment: Are both people actively choosing to invest in the relationship when life becomes difficult?

None of these questions provides a diagnosis by itself. Relationships can move through temporary periods where one component becomes harder to maintain, particularly during illness, grief, parenthood, financial stress, career changes or other major disruptions. A temporary decline in passion does not automatically mean a relationship is failing, just as strong commitment cannot automatically solve every problem between two people.

The value of the triangle is that it turns a vague feeling into something more specific. Instead of simply thinking that a relationship feels different, someone can ask whether the missing piece is emotional closeness, romantic intensity or the shared decision to keep investing in the relationship.

Love Can Survive A Weak Side Of The Triangle

A relationship does not need all three components operating at maximum intensity every day. Passion can rise and fall, intimacy can become harder during stressful periods and commitment can be tested when circumstances change dramatically. Long-term relationships are rarely emotionally static, and expecting them to remain identical to their earliest stage can create its own set of problems.

Sternberg’s theory offers a way to understand those changes without immediately treating them as proof that love has disappeared. Two people can still care deeply about one another while recognizing that something has become weaker. The important step is being able to identify what has changed rather than quietly allowing the distance to become normal.

That may be why a four-decade-old triangle continues to be useful. It takes an enormous and complicated subject and gives couples three concrete words they can actually talk about: intimacy, passion and commitment. Sometimes the biggest relationship problem is not that the love has vanished. It is that nobody has found the words for what is missing.

Sources:

1. Sternberg, R. J. (1986). A triangular theory of love. Psychological Review, 93(2), 119–135. https://doi.org/10.1037/0033-295X.93.2.119
2. Acker, M., & Davis, M. H. (1992). Intimacy, passion and commitment in adult romantic relationships: A test of the triangular Theory of love. Journal of Social and Personal Relationships, 9(1), 21–50. https://doi.org/10.1177/0265407592091002
3. Sorokowski, P., Sorokowska, A., Karwowski, M., Groyecka, A., Aavik, T., Akello, G., Alm, C., Amjad, N., Anjum, A., Asao, K., Atama, C. S., Duyar, D. A., Ayebare, R., Batres, C., Bendixen, M., Bensafia, A., Bizumic, B., Boussena, M., Buss, D. M., . . . Sternberg, R. J. (2020). Universality of the Triangular Theory of Love: adaptation and psychometric properties of the Triangular love scale in 25 countries. The Journal of Sex Research, 58(1), 106–115. https://doi.org/10.1080/00224499.2020.1787318