My daughter's father has not seen her, and does not call. She is now 6 mos. I have been in a relationship with another guy since I was 2 mos. pregnant. This is the only father she knows. What should I do about her birth father?

It really depends on lots of things. Does he want contact? Do you want him to have contact? If he is not having contact at the moment then I would treat it like you would if your baby was adopted ie baby you have a birth father and a father who is bringing you up. If you guys are really serious then maybe your partner could adopt her. I am sure that if you tell the people here a bit more then they will have some more advice for you
Take Care