Why are girls mean to me, but without actually being mean?

Every single girl I've ever liked in my entire life has lead me on for months, and even the one I brought to the homecoming dance disappeared after we got there, reappearing only for a ride home. It doesn't happen with any of my other friends, only me. I just feel like dirt, because I think all these nice girls are interested in me, we're friends one day and suddenly she's ignoring me. I don't even like ask them to be my girlfriend, it's just completely out of the blue.