You need to stop obsessing and move on, the thing you thought would, now is never to be, you have to embrace that reality, otherwise you will drive yourself into the depths of despair, and clinical depression, you don't want to travel that road, it's dark and foreboding, and I speak from experience, I've been there, and it took me longer that it should have to climb out, but I did, and I'm free now, and you need to be free.
The thing that I realised was it wasn't my fault, and the loss of her is a state of mind that you continually bring yourself back to.
So stop punishing yourself, and realise that you have attributes that you can give to another person, a person that will love, and care for you, trust me, she is looking for you right now, but can't find you, and she can't because you are wallowing in your own self pity, and making yourself unavailable, so move on, accept that the past is gone, but the future remains to be discovered...
whatever you did or she did or whatever happened was prob really bad that of 4 years of being engaged you broke up. you should really they makin things right if it hasn't been to long. if it has then you probe have to move on cause if she hasn't come back all that time ago than you have to get in your mind thats she's not coming back
Go and see her. It sounds to me like you have her better in your head than she really is. You will see she isnt and be able to move on I did this. I went back with my high school sweetheart after missing her for 18 years. I loved her so much and we broke up. Now I'm with her and so happy. Bad example. Sorry.
See, that is the drawbacks of waiting to long! You say this girl was your fiancée, for 4 yrs. You made her wait too long! A fiancée is a woman you have promised to marry, not live with for unmeasurable amounts of time. You should have set the date, and acted on it. Now, she is probably someone elses imaginary fiancee. =(