Boyfriend going to party

I’ve had trust issues with my boyfriend in the past but he’s earned it back. He plans on going to a girls house party friday and it pisses me off so bad. Im trying not to go off on him and im trying to say calm thought in the inside im blasting with anger. I dont go to parties and i dont want him going if im not (me and him both aren’t party people so its suspicious). Just imagining him being there with another girl makes me wanna snap his neck.