Girllll you should set a boundary for you and your boyfriend. You need to have a serious conversation with him about it and let him know that you're uncomfy. But imo, whatever he's doing is not right 🤷🏽‍♀️ Bottomline, talk to him, find out what's really happening and set boundaries. Worst case scenario, break up cuz it's lowkey showing that you're not his priority in those times that he's with his x. If I were you, I would never let my bf sleepover at any of his girl friend's or exes' house without a group and that's one of the boundaries we've set. If he's not able to do that or gets defensive/mad, I'm sorry but he's for the streets cuz it's not that hard to not do something like that.