Breakup? or no? help/read

Me and Mitchell have been together on and off for over a year.
1-14-13- first dating
6-08-13-first breakup (2 days)
6-10-13- back together
10-11-13 -breakup
11-23-13-back together
3-9-14-dont even know anymore :/

One of my best friends always commented on how hot my boyfriend was...and that if we ever weren't together they would date, I got on Mitchell's Facebook the other day. He lied to me about remembering his fb login and such. But I guessed his password and was getting ready to post
pictures when two conversations came up, one from my best friend and one from a girl who he dated when we broke up in October. I went through the messages with my friend when I came to a halt, they were talking about me. BEHIND MY BACK. He told her how I depressed him and how I never let him follow his dreams and how he is hiding a ton of shit from me. I bawled my eyes out. I instantly started reading the messages from Kassi. They were talking about how she needed to talk to him and how it was urgent and how she couldn't wait.. Then Mitchell found out I knew his password and changed it and kicked me off. I got back onto my Facebook and unfriended everyone except for Mitchell, Nick(like a brother to me and is Mitchell's best friend),Carter(a friend from Elm.),Gerald(amazing cx), and a few others. But now Nick is dating Allison (the "friend" who talked about me behind my back) I am so close to breaking up with Mitchell again.. he always does this where he talks bad about me behind my back..
Breakup? or No?
I really need help deciding because I love that family and still love him. I think. Heck, I was even there to name his baby sister Carina.
Please HELP!