My boyfriend is constantly getting mad at me about my past!!?

How can I deal with this....My boyfriend obsesses about my past. I try to ignore him, i tell him i love him and only him. I say to let it go it was before him...he doesnt stop! He is relentless. I unblocked my ex from my facebook and he is freaking out!! It was months ago and I am not angry anymore. I love my boyfriend...but he is constantly brining up my past. He actually cheated on me kissing someone else a month ago and we have really tried to overcome that. He has done a lot to prove to me it is only us. But he is just constantly getting mad at me about anything from my past accusing me of lying! Please help! I dont know what to do