Help me 😭😭😭 I need advice

So, my boyfriend broke up with his ex roughly in September and they were together for about 1 and a half years, and I broke up with my ex in August and I dated him for 2 years, me and my boyfriend have been dating since December. And well sometimes I get this heart ache and can never stop thinking bout him and his ex, cause they legitimately fucked like 4 times because he told me about it since I asked, and well I never did any of this with my ex so sometimes I get really angry at my boyfriend for no reason over his past, but his ex treated him like complete shit, she cheated on him whenever he went out of state, and she was just so stupid for giving up such a diamond. She broke up with him and got back with HER EX and she still has the audacity to try to talk to my BF and "be friends" and it gets me more mad considering he's in drama class and has to act in a play with her and she even came up to him to ask him if he's cool with it even though he has no choice in working with her and I'm at the point in where I don't even want to watch it because I hate her sooooo much. Am I over reacting? Or do I have every right to hate her?