I am thinking cohort. People tend to date people who hang out in the exact social circles as they do. Which is what happened in this case, really.

There are lots of token and outsider members of colleges and frats that the insider groups will never even notice. The person dating the boss or the bosses' daughter/son is more likely to be a member of an insider group than somebody who attended the same elite university at the same time - especially if the frat/college person is of a different race or economic class than the boss.

Went to the same school, in the same frat, from the same town, went to the same camp, dated your sister once are all shorthand for describing insider groupings, not the cause of them.

People who work hard who are not insiders in that way will resent it.