<human>: Could you distill the essence of the text into 1-3 sentences?

I am in a pretty bad place at the moment Reddit :(

I live in a pretty small town on the east coast and haven't had much luck with relationships. I always seem to have been giving advice to my good friends on their boyfriends and I go crazy when I see them dropping perfectly good relationships just to run off with their old flames just to end up back where they were. 

I was in a 2 year relationship with a guy who I was perfectly happy with. He was good looking, caring and treated me like a princess. 
 My ex (Lets call him 'S') got back in touch with me a a few months ago. (We broke up because, frankly he was a scumbag who always treated me like shit and upset me constantly.) but I realised I wasn't over him. He seemed so sweet and assured me "he had changed" and wanted to give this relationship another shot. 

As much as I loved my boyfriend (lets call him 'M')...It was dragging up some old memories and making me really confused. I decided to call it off with 'M' and try to see what happens with 'S'. As horrible as it seemed, I couldn't carry on with him knowing I had feelings for someone else...

Fast forward a few months later and 'S' has gone back to his old ways. We have broken up and he has made me feel like shit, AGAIN. He basically just wanted to get me back for no other reason but to fuel his ego and 'M' won't talk to me now because he has found out that I broke it off to try things with my ex again. He won't return my calls and has told me he doesn't trust me. 

What do I do? Im at a complete loss :(
<bot>: Was in a perfect relationship, got back with ex. Feel like I've ruined the only shot I had at a happy relationship.