I think I'm falling in love and don't know what to do?

First, try and understand why your mother hates him and see things from her point of view. If you can do that, then hopefully you'll either see why you shouldn't date him or you'll be able to persuade to her that he's not that bad. If you can't do any of this, then just tell your mother that you're going to give it a go with him again, what ever she says. It's your life, your feelings, and, if it comes to it, your mistakes.

DON'T go behind your mother's back, because that could spark some serious long lasting trust issues which could permanantly damage your relationship with your mother.