how do you deal with a sudden breakup?

My boyfriend lied to me about his past a few months ago and obviously I've questioned a lot he's said since then. He hated it. Everything to him was an accusation and I always wanted him to see my side of things so he'd hopefully understand and we'd stop arguing. I questioned about a girl two nights ago and he said it would have to stop or else we'd have to break up. I said ok. Well yesterday morning he had his mind made up and didn't give me a chance to say anything. He just said he was set on