This seems to be an age old problem. You're not alone in getting attached to casual partners, in my experience it boils down to one of two things...lack of self confidence or a constant desire for approval/love. I know this because I'm guilty of both aspects.

All my life I've found partners on the internet, there are 2 exeptions. The first was a friend of a friend that just did not work out and the second I met at a gig, that was more than 2 years ago now and we're still together. Looking in obscure places (admittedly a gig isn't that strange - but it was for me) sometimes pays off.

I think you should stop trying for a while, as the more you do it, the more attention you'll crave and the more rejected you'll feel if you don't get it.