Advice...Ex and I had a child then he had another one by another girl just a year later?

I just don't know what to think about this whole thing. We are going through custody issues right now. We were never married but we have a one year old. I know I messed up and I will never do that again. I am not one of those trashy girls who just keeps on popping out babies. I am going to abstain from until I am married now. I am 23, he is 24, and his girlfriend is 18. I was not told about their child until last week and it wasn't my ex that told me, it was one of my friends who saw them come into a restaurant with the child. He FINALLY told me about it yesterday but only because his other child, they found out, is a carrier of a hereditary health issue. He didn't know if our child could have it. That is the ONLY reason he told me. Do you think that this new child will affect custody? He has not been paying child support on time and just has not proven to be responsible. How in the world are you going to care for 2 children when you can't even support one??? I am just so confused. His girlfriend doesn't like me and I am scared she is going to treat my child differently now that she has her own. I don't want my child to be like Cinderella, that's just not fair. Any advice? Will it affect court?