It's more than just propinquity

Is there a term for the mutual romantic affection for another person that develops as a result of continued or repeated proximity or encounters. I was hoping that "propinquity" would cover that effect, but that only relates to the situational nearness.

Solution 1:

It's called the Propinquity Effect

The propinquity effect is the tendency for people to form friendships or romantic relationships with those whom they encounter often, forming a bond between subject and friend. Workplace interactions are frequent and this frequent interaction is often a key indicator as to why close relationships can readily form in this type of environment.1 In other words, relationships tend to form between those who have a high propinquity. It was first theorized by psychologists Leon Festinger, Stanley Schachter, and Kurt Back in what came to be called the Westgate studies conducted at MIT (1950).

Incidentally, propinquity in social psychology refers to physical or psychological proximity. … It can mean physical proximity, a kinship between people, or a similarity in nature between things ("like-attracts-like"). Two people living on the same floor of a building, for example, have a higher propinquity than those living on different floors, just as two people with similar political beliefs possess a higher propinquity than those whose beliefs strongly differ.

So, propinquity it is, after all.

Also, in interpersonal attraction, the more often someone interacts with a person, the more pleasing and likeable they find that person. That's the familiarity principle (mere exposure effect).