Complicated boyfriend question.?

I'd definitely stay out of this one. As tempting as it would be to put this girl in her place, actually your boy should be the one to grow a pair and stand up to this girl. Talk to him about how you're feeling. Explain how much this is bugging you, and ask if for your sake he might block her as a friend on Facebook. Honestly, it sounds like both of you could do without this extra drama. Exes (especially ones that still keep in constant contact like that) are nothing but trouble. Trust me. It can be difficult to talk about something like this with him because past relationships are usually a touchy subject, but if he loves you he will at least listen to what you have to say.