I can relate... my ex left me a year and a half ago... I haven't had much (Read: Any) luck since mostly due to a combination of bad looks , student loand debt, and [very] poor self esteem. I'm the first to admit these things, but this is after the fact I started to look at / realize them... Truth be told, when I was in the relationship, I was happier, more focused on my future, more focused on making myself a better person all around... since she left it kinda left me questioning my life choices all around. It's been a year and a half, and she's dated other guys (Read: Many other guys) and her last words to me were: "No girl will ever give you a chance, hell I was just settling until something better came along".
Sure, many people here will most likely say "I'm better off without her" or "I can do better", but I don't see it like that. not just because of my self esteem, but because I've never done better than that... That was the first relationship I had ever been in, it lasted for about a year, and i'm now 27 years old... all my friends are married / getting married, those who aren't are dating / living life... and I'm just working... eat sleep work... There's nothing to do around here without spending assloads of money, and internet dating has only brought me creepy overly attached girlfriend types as well as developmentally challenged girls, as in legit IQ is less than 100. (Hey, i'm being honest...) I realize i'm balding, I realize i'm overweight (I'm trying to fix that one but nobody cares what you're TRYING to do or how hard you try)... I realize i'm saddled in enough loan debt I could have bought a house... but I guess as one girl told me: "You're not only unattractive, you're undateable".
and the whole reason my ex left me? That I was being "Paranoid" that she was cheating on me [again]. She had cheated on me, with several guys in a one month period... I found out, and I forgave her / moved on... and then a few months later, she started acting all secretive of where she was / what she was doing... bought a 2nd "prepaid" phone she was using for "work" allegedly (she worked as a babysitter / housekeeper). and the icing on the cake, was constantly hanging out with this guy and "oh i'm spending the weekend there, don't worry he's gay". (Yeah, facebook photos of her making out with him, he's totally gay...) when I brought that up, she dismissed it as her being drunk, and then left me, stating I was being "too paranoid" for her... So yeah.
tl;dr: My Ex cheated on me, then left me after I couldn't trust her months later when she started cheating again... I'm still not over her mostly because of the "good times" we did have, and I realize I may never get another chance in life at this point.