Self-worth isn't black and white. Just because you don't always appreciate your own worth and your own contribution to your family and community, doesn't mean you feel completely worthless. In fact, no one ever really appreciates their own worth to the fullest - at some point we all need someone else to tell us what we mean to them. In this case, though, you're clearly expecting this girl to validate you in some way, whether to acknowledge your crush on her or just to acknowledge that she has no feelings for you. You keep putting yourself in positions where she might do either and that creates this endless loop of infatuation that keeps you from moving on.