Boyfriend went through my facebook without permission?

Back in June, I broke up with my boyfriend because he was constantly being a jerk. Derogatory comments all the time, always judgmental, constant profanity, never affectionate, etc. I basically dropped all his stuff off at his house and left him a note and then went on vacation with my family. He called constantly and wanted to get back together.

After I got back from vacation, I was trying to distract myself from the temptation to talk to him, and replied to a personals ad a guy put out who was new to the area and just looking to get to know new people. I posted on my Facebook about it, because I thought it was funny he had his parents come pick him up after 2 beers.

I ended up getting back together with my boyfriend shortly thereafter, and we've been back together since. Well about 2 weeks ago I left to go get food during a baseball game and it took forever. I was drunk and didn't realize how long I'd been gone and when I came back he wasn't there. Then he called me and started calling me a wh*re and s*ut and c*nt. He said he was done with me. We fought because I had no clue what his deal was suddenly. When I came back to the hotel room and found him he yelled and called me all the same names. When I went leave he said "what, are you trying to get passed around again tonight???" and said he knows I'm seeing other people, and that he went through my facebook! He went through all my private messages and posts and profile and everything.

I still don't know how he got into it--all I can think is I must have accidently left it open.

I said I didn't want to break up with him and he said he can't trust me because I'm "seeing other people." We were broken up, and the guy and I literally just talked for like an hour.

I told him he can get on my facebook any time because I have nothing to hide and gave him my password. He doesn't have a Facebook--he says that it's for idiots and wh*res. And now he makes comments every day. Like "why don't you have a relationship status on there?' "Why is your address on there?" "where are the pictures of US?"

Do I have a right to be offended that he went through my facebook without my permission, or is he right to be mad that I met someone else after breaking up with him?