I'm married and this lady is married and we had sex unprotected sex. She said she was on the pill, but you no how that goes. She was sleeping with other guys before me. I really believe the baby is not mine. I just have this gut filling. Anyway, if she is married still to her husband what obligation to I have to supporting a baby that may not be mine.

After the baby is born and she claims you are the dad you demand a paternity test.
Do not sign a single thing like acknowledgment of paternity or the birth certificate unless the tests come back You ARE the father. Then if you are and she goes after you in court then you will have to pay child support.
Quite likely she will have her husband sign the birth certificate so she isn't 'caught' and you will have no obligations