Twins dad is trying to get into the picture, What should I do?

He left when I told him I was pregnant. He went around telling people that they weren't his kids. I know that he needs to be in their life but should he. He wasn't there the first three months. Why should he get to be in their life now. I don't want my kids to have to go though this. He might decide he doesn't want to be in their life when they are older. I know how that feels and I don't want that at all. I really need some advice. I know coming up here isn't good but I know there are some good people out there. I just need to know if I should let him be in their lifes or what?