Is love or friendship a relationship?

To be specific, neither love nor friendship is a relationship.

A relationship refers to the linkage between anytime (non-living/ living things)
For people's term, the relationship is known as interpersonal/ social relationship

Friendship

Causes

1. Interpersonal Attraction -- personal preference, physical/ sexual attractiveness
   
2. Proximity - distance
   
3. Familiarity
   
4. Similarity -- Interest/ Perception
   
5. Complementarity -- Gender/ perception or character
   
6. Reciprocal liking

Even though friendship looks simple and easy, it is vastly complicated. If we used the different personalities of different people to explain friendship, it will shows a lot of complication. Therefore there are theories that explain how friendship works or develop.

There are 4 main theories that shows clearly what is friendship.

1. Equity Theory --- fairness/ fair treatment. Give and take
   
2. Law of Attraction --- Like Attracts Like, related to Law of Gravity
   
3. Social Penetration Theory ---Closeness involved self-disclosure
   
4. Mere Exposure Theory --- friendship is gained through familiarity
   

Different theories show the different ways people choose their friends and the different stages of friendship. People become closer through communication, therefore if they understand each other well, they may express their personal attitudes and reveal their private information.