Hmm well it sounds to me somewhere along the line you forgot the no contact rule. When a girl backs off you do the same because whatever you've done it can't be won over by persistence. That will just make things worse. The fact she fed you lines such as "your amazing its just me thats the problem" should be your get out clause to begin with. But you baught it hook line and sinker hoping it was all true and she'd come back to you.
You do know when a girl is having problems. She will go to the person she has the most respect and love for to help her through it. This obviously wasn't you here.
I have a girl 'friend' who calls me sometimes when she's having problems. She'll openly admit that's why she called. But she has a boyfriend. Why me? I know she's interested to some extent because well I can read the signs. I have a girlfriend and wouldn't do anything about it so I'd say I'm emotionally unattacthed enough to read the situation.
You don't want to become the guy who is always waiting for something good to happen. If a girl shows uninterest back off and go look for something else instead of coming on here wasting your own time on someone that was never meant for you. I mean what if you died tomorrow you'd be ragin you ruined your last days pining over this girl.
As for expecting her to tell you she is seeing someone else... If she didn't have the decency to tell you it was over in the first place. Why would you expect she had the decency to tell you she was seeing someone else? Which is even worse?
You have been taken for a ride and you should know this by now. If anything I'd pick up what's left of yourself respect and cut ALL contact. She isn't worth a thought the way she's treated you. You deserve better.