Why? If you're willing to go out of your way to tell his family about it, you should do the same to your boyfriend. Are you gonna tell your boyfriend's family too? Since you're "so fucking angry right now".

You are directing righteous rage too narrowly. You are willing to try to hurt this person yet showing grace and acceptance to your bf.

This makes you arbitrary and likely just enables you to keep some relationship going that you know should be ended.