I think it is always good to maintain a relationship with the child's father, unless he is very abusive of course. Obviously, not dating wise, but it is good for a bond to be made between father and child. Even if the relationship is spotty, it can become great in adulthood, or may eventually flourish earlier than that. Just raise your child without having too high of expectations of dad and be casual about it.
I have a friend who had an absent father, and now that he is an adult, they have a wonderful relationship now and he is a great grandpa. That wouldn't have happened had the mother cut him off in the child's life, even though he was a crappy dad back then.