Can't Hold onto a Girlfriend?

Okay, a little weird, but here goes :] I'm 29 and am currently single. For the past two years I have had trouble getting keeping a girlfriend. The first one was dating someone else, but she found me irresistable, we had sex and afterwards she went with her boyfriend and matrried him. The next one was a french girl who again thought I was amazing, but she said she liked to go out clubbing and kissing other guys..I thought this was weird, and told her so, but she said I was being jealous and I was promptly dumped. A week later I met a girl from Russia who was stunning. Again she was dating someone, but we met and she went off with me and we had amazing fun. Sadly when I questioned about the other guy when we first kissed, she said what about him... I can have you both. I made her dump him or I wouldn't be around. She did, but I never forgave her for making me feel cheap. I was promptly dumped again. A month later I met a girl from london and again she was dating someone else, but she had liked me for ages. We got together, then after a week she dumped me as i was too intense, only to come back a week later and we were engaged and living together, That lasted a year, but she dumped me after I found out she was looking on a dating website for someone else. That was in feb this year. Then, a month ago I met a woman with 2 children and she fell in-love with me so quick that it scared her. she backed off and never came back. Funnily enough, a few women have said this to me and I don't know if its a lie or not. I am told I am good-looking guy - I apprently looks like Tom cruise, kevin costner, etc and am told I am incredibly charming and funny. But... why am I alone? I am told I am the most amazing person ever by these women, but am dumped shortly after. I am a good-guy deep-down and would love to get married and just settledown wih kids. Please help.