you didnt know and most probably he didnt know as well. you are/ were his strong pole. thats why he came to you.
if you feel so bad about his ex you should come clean. why dont you just go there, together with him of course, and inform her about all the things you both know now. sometimes explanations help most, she can then get on with her life and you probably feel better about it.
its very natural for a survivor to get rage, anger...and just think of it as an angry teen. control issues are essential for a kid (not grown, not developed - the chances were taken from them by their f...up abusers)to have control. all you need to do is to show him that he doesnt need to control YOU, he has you under control due to your love (if its still there). he just wants some safety and he doesnt feel safe. he needs you to be there for him and he needs you to be able to be fully honest to you. if he can talk anything to you, you can help him over this and if you lose him in the end, then thats the risk you take. it does happen, but not always. if you still love him, read more, talk more and make sure you understand him really.

everything is always okay in the end, if it's not, then it's not the end