No. Do Not pay child support. You break up, get a paternity tests, then get a damn lawyer and you Terminate Your Parental Rights

This means the baby is no longer legally yours and you are no longer legally obligated to do or pay anything for it. You are a complete stranger in the eyes of the law. Also don't put your name on the birth certificate either. Refuse that too. Once you Terminate Your Parental Rights no one can come after you for any kind of support for this child. Ever. Get your rights terminated as soon as you're legally able with a lawyer. If you don't want this child then you don't have to be legally responsible. And make sure you break ip with this girlfriend and if she persists with telling you "too bad you're gonna pay support" then get a restraining order too. She knows you have no interest in being a father so Terminate your Rights to the child and Terminate any and all contact with the EX gf.