I'm needing some advice.

So, my boyfriend and I have been dating for about three years. This past week he was acting a bit weird. I could tell something was wrong. He was very distant, and he's never like that. I was concerned so I tried to talk to him and he didn't want to talk, so I didn't bother him. I talked to one of his best friends because I was worried about him. No one knew what was going on, but he told his friend that it had happened before so not to worry. Instantly I began thinking of what it could be. I had something in mind, there was a girl that he used to have a thing with a few years ago, she came to visit while we were dating and he hung out with her and didn't tell me about it. She expected more, as jn hooking up, but he respects me and would never cheat. I thought that she came again and he was possibly having mixed feelings about it. Last night he left his computer at my apartment, I was curious to see if I was right, and I was. I shouldn't have snooped, it was wrong for me to do that, I know. I told him about it and I was very honest. I apologized. He told me that I didn't trust him and now he doesn't trust me. He completely turned and got mad at me. I wasn't even mad about the girl, I was just upset that he was hiding it from me. Now he wants to take a little break..... Any advice?