I don't think there is alot you can do until the baby is born. My ex bf had this problem w/ a girl after me..He filed for a paternity test to prove he was the father before he handed out anything..If I were you, I would be looking into your rights (if you are determined to be the father). Don't get all assy about things b/c it makes you look bad dude!
Another option is to give up your rights! If you are the father and you give up your rights, you have no obligations..I think this is true for all states..not sure..Every state has different laws.
If you are the father and plan to be in the baby's life...which personally I think you should if you can..you need to keep yourself together and focus on the baby and less on her! The baby can be influenced by conflict between you and his or her mother..Just b/c their babies doesn't mean they don't sense and feel whats happening around them. My parents divorced when I was about 11 yrs. old and I thought things would get better..but they only got worse! When I was at my dads, all he did was down my mom. And when I was at my moms, all she did was down him b/c they couldn't stand each other they put myself and my brother in the middle of their problems, anger, and jealously! They should have been more focused on raising us and loving us!
Just try to do your part and keep things as neutral as possible for the babys sake. Don't let her step all over you..But don't make yourself look bad..If it's possible, try to talk to her outside of court, maybe you two can come to an agreement if you and her can get along long enough to talk like two normal adults.
As far as her personal life goes, don't let that hender you..don't worry about it..ignor it..unless she is hurting the baby in some way.
Pls, for the babys sake..try to be as peaceful as possible! Assure her that your focus is only on the baby and don't throw her whoring around in the mix..that will only make her worse!