<human>: I'll keep this short. I was dating this girl and it was going exceptionally well for about 6 months, just mutually head over heels, until we started living in different cities and had to break up due to a lack of contact. I was also secretly suspicious of infidelity, and I never really found out why she changed her mind about the whole thing.

This was devastating to me because she had already had me thinking we would be getting married just as soon as we could and eventually have kids too (it really was exceptional for those 6 months). After some failed attempts at staying in touch platonically, I decided the only way to get over her would be to cut her out and end all communication, so I did.

But despite my best efforts and the passing of 3 years, I still think about her, want to talk to her, or get flashbacks all the time. And it affects my life in that I've been terrified/incapable of getting into an emotionally committed relationship ever since. 

My question is: What should I be doing/what am I doing wrong?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Had a short but powerful relationship with a girl that ended after we moved to different cities and she became nearly impossible to reach. Still not over her. What the hell is wrong with me?