I'm In Love With My Stepmothers Younger Brother?

Well its not incest so that's in your favor, but families are generally against such unions and your age difference is also a factor here. Your parents might be against that too. I think the best thing to do is wait until your 18 and legal and then see how you feel about each other. At that point even if the parents were against it you would be free to do as you please.