I'm dating someone who is great and should be perfect for me. However I can't get someone else out my mind and it's driving me nuts. It makes no sense at all as the girl I'm dating is infinitely fitter, more sophisticated, educated etc.
Other lass has issues I think. Her faults just make her more attractive but she's already brushed me off twice. I think she just has low self esteem. :/
You have White Knight/Broken Bird syndrome. You find the other woman attractive because she's someone broken you can fix. It makes you feel needed, even though she doesn't want you.
You're better off sticking with the better woman who can actually be an equal (or better) partner in the relationship with you. The question is, do you want someone that can make you happy, or someone that will give you drama?
Stop thinking about the broken woman, and give the better one the chance to make you fall for her.