@ippn1,
On the long run you probably wouldn't have been right for each other anyway. Judging from just the bits of information here, I'd say you two probably were too different. (It seems like you do judge her on the basis she wanted to have sex after the 3rd date, for instance, which means there were some fundamental differences right there).
There's nothing wrong with seeing sex as a part of loving relationship only, but if you date a person who considers it to be just a physical act, you will probably have some issues down the road. For instance, her sexual past probably would've scared you (if she had told it to you) because even if to her it's just been a series of more or less meaningless acts, you would've seen it as her having shared an act of love with all these other guys.
Somebody else already said that because she still had feelings for this other guy, the outcome would've been the same anyway. I agree. Actually I think you should be happy you didn't sleep with her because you probably would've become more emotionally invested in the relationship if you had, and the break-up would've been even worse.