Broke up with my bf of two years two months ago. What do I do?

We lived together for a year. Things started falling apart in the summer and he told me he wasn't sure about us anymore (I remained in contact with my ex and this really upset him). He left me, but I begged him to stay, telling him that I can't live without him because I loved him so much. I stopped talking to my ex, things seemed to get back to normal until I found out that he was with another girl in the 2 days we were broken up. Worse yet, he secretly continued talking to her when we got back together. We kept on fighting after that almost every day until we finally officially broke up in the winter.

We didn't speak for a month after that. But recently were drunk dialing each other every weekend and seeing each other in secret. Until I broke it off because it made me feel angry every time because it prevented me from moving on. He kept on telling me how he loved me so much until I destroyed him (by talking to my ex, I'm guessing). However, now that we haven't contacted each other in more than 2 weeks, and I am somewhat getting a clearer view of things... I really am suspicious of that he used that excuse to manipulate me (because he had some sort of an emotional crisis where a part of him wanted freedom and a part of him was afraid of losing me). I didn't talk to my ex that often. One text or two a month, if even that. Those were simply "hey how have you been" texts. I never saw my ex, nor did I ever hide anything from my bf. I think him hooking up with that girl is much worse than random meaningless texts.

Long story short. It has been two extremely long weeks. At this point, I am debating whether I should stop dodging potential new relationships. I'm just too scared to get into anything because I don't think I'm over him and I wouldn't want to hurt anyone by getting into a relationship while having feelings for my previous bf. As for him, he seems to be all over the place. I don't even recognize him anymore - he gets drunk all the time, there's various photos of him and new girls, he was still seeing that girl from the summer (he told me, when i confronted him about it while we were doing whatever you want to call it thing after out break up, that she was just a distraction), and other girls. It's like a dog off the leash (kind of makes it easier in some sense for me to move on, because the behaviour is unattractive).

Another odd detail... his friends seem to be much friendlier with me. They keep on talking to me. Especially his best friend. what does that mean? We never used to talk while I was dating him.

At this point, it's head vs heart. I could pursue my ex, I could be that sad little puppy running after him until he changes his mind and stops his childish behaviour... but what would that do? Even if we did get back together some day, would things be ever the same? Would we have the same strong feelings for each other? I dont know. Yet, there's a part of me that is constantly in the way of my well being. I think of him... it's actually embarrassing how much I think of him every day. That has to mean something.

What.do.I.do?