This study was mentioned in the paper sometime ago, just found it online. Basically, researched tracked sexual relationships in a Midwestern high school over 18 months.

A study of sexual and romantic relations at a high school found students connected by long chains, rather than in a tight network with a core group of a promiscuous few.

Sharing of partners was rare, but many students were indirectly linked through one partner to another and another.

Here’s a few more details but if you really want your eyes opened, check out the map of high school lovers.