The triangular theory of love was proposed by Robert J. Sternberg.

Sternberg believed that there are three distinct components of love: passion, intimacy, and commitment.
These three components form love like the three sides of a triangle. This is why it is called the triangular theory of love.

Passion refers to the deep physical attraction and thoughts about a person. It also involves the sexual urge and arousal of a person in relation to another person. Intimacy means the feelings of closeness, liking, and emotional attachment to a person. Commitment means the level of connectedness that is characterized by the desire to stay for a long time in a relationship. In other words, it is the desire to remain committed to a relationship to keep it unbroken forever.

The above three components come together in different combinations to form different types of love. This is because the type of love keeps on changing with various factors such as the age of the relationship. For instance, passion and intimacy may be initially greater in a relationship, but as the relationship proceeds to a level of seriousness, commitment also increases.

Following are the types of love depending on different combinations of its three components.

It is that type of love where a person has the feeling of closeness and emotional attachment towards another person but not the feelings of passion and commitment towards that person. In other words, there is intimacy but not passion and commitment.

It is important to understand that these three terms (intimacy, passion, and commitment) are generally interpreted in more or less similar meanings (particularly the words intimacy and passion) but this theory distinguishes among these three terms to give a clear meaning of each term: intimacy (feeling of closeness to someone), passion (physical attraction to someone based on sexual urges) and commitment (desire to sustain a relationship for long). Therefore, the terms intimacy and passion may not be confused with each other. 

This type of love is based on intimacy but not on passion and commitment. The example is love in friends where a person feels emotionally attached to another person, but no feeling of physical attraction or sexual urge is involved.

Infatuated love is characterized by passion while intimacy and commitment are absent.

In this type of love, a person is physically attracted and sexually aroused towards another person. It is characterized by a high level of psycho-physiological arousal. Another characteristic is that this type of love happens very quickly. For instance, if a person sees another person (to be attracted towards), he at the first sight may experience a fast heartbeat and hormonal changes and thus, develop an intense feeling of love for the person.

The term infatuation means a strong feeling of love, but which generally does not last long. Though it is a strong love but also a short-lived love. This type of love does not last long because it lacks the other two important components of love which are required for maintaining the relationship for a longer time.

It is that type of love where intimacy and passion are absent, but commitment is present. Generally, in an old relationship that is continued from a long time, the intimacy and passion may be lost but the partner decides to remain committed to the relationship. With the passage of time, the partners may lose feelings of physical or sexual attraction towards each other, but they still want to remain together in the relationship.

However, it is not always true that with the age of the relationship, the relationship slowly and gradually moves towards empty love. In some relationships, it can be the end of love whereas in other relationships it can be the beginning of love. For instance, a arrange marriage may begin with empty love but later on, passion and intimacy start to become part of the love. 

Romantic love is purely based on passion and intimacy. It generally lacks commitment. In such a relationship, a person has a deep feeling of emotional closeness (intimacy) and physical attraction (passion) towards another person.

This type of love is a product of intimacy and commitment but does not involve passion. This is a close relationship where the individuals feel emotionally connected to each other and want to sustain their relationship forever. In such a relationship, the individual enjoys the company of each other, but no sexual expectations are involved. For instance, deep friends who provide psychological support to each other in the form of care and respect.

This type of love can also be seen among the family members (e.g., brother, sister, mother, father, children) where the love is purely based on care, respect, and commitment towards one another. 

Fatuous love is that kind of love that consists of passion and commitment but not intimacy. The person is physically attracted to another person and due to this attraction, the person desires to maintain the relationship for a long time. It generally lacks intimacy – the feeling of psychological or emotional connectedness – and the relationship primarily revolves around passionate desires.

Sometimes the love-marriages are simply a product of fatuous love because of severe passionate desires, the partners decide to enter into wedlock to be able to maintain their relationship forever. However, since the important component, intimacy is missing, some of such love-marriages may end up in separation or divorce after some time. This is because the passion fades away with time and there is no intimacy to protect the relationship from breaking.

Consummate love is that type of love that comprises all three components. It represents an ideal relationship because each of the three components of love is equally important for a healthy relationship. Like a triangle completes when it has its all three sides, when the three components of love combine together, it can be called a complete love.

This type of love is usually difficult to achieve but when couples establish relationships based on consummate love, the expression of all components of love helps them achieve a successful and happy relationship. However, consummate love is also not always permanent because the passion component may fade away with time. Therefore, though it is an ideal form of love, it is difficult to form and maintain.