Confused

Ok so my husband and I have been together for 6 1/2 years, and married for 3 1/2. It hasn't always been easy, and a couple of years ago I found out that he cheated on me. I could tell that he was truly sorry for what he had done and based on his family life growing up I was pretty sure it would never happen again, so we decided to work through it. We dealt with his infidelity, and moved on with our life. Fast forward to now... I found out yesterday that she is saying that her daughter is his. When she was pregnant with the baby she had an African American boyfriend(the baby is white), and he has been raising the baby up until recently. Well, they just broke up and now she's coming for my husband wanting money. She knows that my husband comes from a family that owns a business, so I feel as though she may only be coming around again for money. The thing is that he slept with her in mid February, I found out on March 6th. He called her in front of me and broke it off. The baby was born on January 25th, and is now around 8 months old. My husband claims he was protected when he slept with her, and obviously the timeline doesn't add up. Other than his obvious lapse in judgement, my husband is a great man. He has helped me raise my son from a previous relationship, and has always been a great daddy to him. We are having a paternity test done next week and if he is the father, obviously he is going to step up and be responsible for his daughter. The child's mother is a drug addict that doesn't have a job, stable place to live etc. If the paternity test comes back that the child is his, he will be going to court to fight for custody of the baby. My husband has spoken with her parents, and they would rather the baby live with my husband, rather than live with their daughter. It honestly has been such a slap in the face for me because we have been unsuccessfully ttc for a few years now, and have recently had all the tests done and are on our 3rd round of clomid. Obviously we will be taking a break from ttc until we figure out where to go from here. I'm not selfish enough to try to bring a baby into all of this dysfunction. As of right now, leaving him isn't even a thought crossing my mind, because I already knew about the cheating, and we dealt with that. I'm confused though about how I feel about this whole situation, and the possibility of being a step mother to this poor baby. I feel as though I could love her as my own if she is his baby. The child deserves better than the environment she is growing up in now, she didn't ask for any of this. Aside from leaving, because that is not something I want to do, what would y'all do in this situation?