Never? Are you saying that you've never ever been attracted (even physically) to any girl?
If this was the case ever since you were young, then I'll have to agree with your claims of being asexual. But if this only started happening in your adolescent years, then I would strongly think that this "indifference" towards the other sex, points to your insecurities about your own looks. Like an extreme case of your ordinary guy calling a hot slutty girl "ugly". But really, he knows he could never get a chance with her, so spurns her first. Except with you, it sounds like it's gone beyond that, and your shutting everyone out for your own protection. Rejecting them, before they reject you.