I would tell your mom as soon as you can. The longer you wait and lie the harder it is going to be to tell her when you finally decided to. He was man enough to stick by your side when you were pregnant. I don't know what else your mom could ask for, a majority of teen fathers leave their girlfriend when they are told about it. Him staying should be an instant sign to your mom that he is a decent guy. Maybe have a family dinner and let your mom get to know him? Good luck either way.