If you REALLY want a boyfriend/girlfriend, you don't get a crush on someone who is already dating someone else. You find someone who is available and seems to be a realistic match for you, and then you go for it. You don't just sit around dreaming about what it would be like if. . .
If you are stuck in crush mode, it's because you want to pretend to be interested when you are really too scared to go for it. So. . . admit to yourself that you are a chicken and that is the first step in the road to recovery.
I like my mole on my left cheek.. anyways.. -mixed signals -rejection -appearing desperate -lack of confidence/shy/timid -feeling like you're way out of there league -another person is in the picture (so competition) -religion/culture -or they know that things just won't work out, no matter what