What is wrong with me emotionally?

Hi ladies! I need some advice here. I've been in a relationship with my boyfriend for 3 1/2 year in which we have broken up 3 times and gotten back together. Some days I'm really happy to be with him and other day when we fight I feel like running away and wish I would have never taken him back when he called. This last time we split up (we were apart for 3 months) I started seeing someone new and it was clear between us that it was going to be a friend's with benefits kind of thing (something I've never done, but decided I'd try since I was tired of the dry spell) and in my honest opinion females can't have sex without strings attached and of course I started having feelings for this guy. My ex called me out of the blue and decided he wanted me back and was super sincere and and said all the right things which still didn't totally convince me but I though what the hell. That same week this guy I had been seeing decided to tell me he was starting to fall for me and wanted to be exclusive and introduce me to his kids. With lots of thought I decided to go back with my ex. Why? I'm not sure. Maybe because it was familiar or once again He convinced me either way I often think of this other guy and what we could have become. The days I'm with my bf now and things are good I'm really happy and the days we fight I want to high tail it far far away. Are these normal feeling in a relationship? He have had a rough past and things have never been great. Is there something wrong with me? Should I be having these feelings? My boyfriend calls me crazy and says I need meds when we fight but in my opinion he get on the defensive when I get mad about something instead of acknowledging the problem. Did I make a huge mistake going back? Opinions and suggestions are much appreciated!