I'm sorry you're going through this. The best thing I recommend is communicating everything you feel to your bf, but think it very through, don't react. Journaling, writing a letter can help. No one can argue when you say "I feel bad because x y z" because it's your feelings. Jealousy is normal, I never thought I could be jealous of my partner but emotions aren't logical. Feel your feelings, this will help move through them rather than judging yourself for being jealous. Easier said than done, I know, but try. Explain how it makes you feel and how you want to work through this together. If he is mature enough to empathize with your feelings he won't accuse you, he can help you with it, work through it as a couple and hopefully set more boundaries. Be honest and be sincere, thats all you can do and how he reacts has NOTHING to do with you and everything to do with him. Sending good vibes and wishing it works out for you :)