It's propinquity. "A factor of interpersonal attraction."
We tend to like people who are physically close to us.
[In ALL possible ways**]
THIS MUST MEAN SOMETHING REALLY PROFOUND.
It reminds me of a teen book I read, wherein the guy falls in love with the girl after she leaps into his car, sits on him and risks being arrested/seriously damaging his car as she speeds away, being pursued by her psycho-ex. The guy doesn't know what's happening, an attractive stranger is on his lap, and he probably liked it. [The girl actually did damage his car.]
They got involved [or at least there was some serious sexual tension] something like a few days later.
Which is a good, very generic equation.
Let t be relative time it takes for the couple to hook up (the lower the shorter)
Let a be their physical proximity to one another from 1-10, 1 being very close and 10 being very far, in the time when they are close to each other
Let b be the percentage of their time that they are not a close to each other expressed in decimal form
Let c be emotional compatibility from 1 - 10, 1 being the most
Let d be the more attractive person's attractiveness from 1-10
Let e be the less attractive person's attractiveness from 1-10
Let x be magnitude of distractions from love from 1-10, 10 being the most
**Well maybe except for blood relations