Maybe the uke getting jealous and the seme rapes him to prove that he only loves the uke. Or maybe the seme getting jealous and he rapes the uke to make sure the uke is only for him.

*if you can give me school life environment, it would be great. But if not, its fine too.

Here is the yaoi with jealousy and rape categories.

Obsession is a drop of water in the desert- crave it, savor it, remember it. ~Unknown