ugh i need help!!!

so my husband's ex girlfriend ended up pregnant while they had one of there many breaks. now she wants to say that the baby is his and he should support it. well I agreed to help her if she kept thing out of the courts. just due to we don't like dealing with court well we got a paper in the mail the other day for child support and a DNA test. I personally don't think he should take one since she got pregnant during there break and the kid looks just like his ex best friend and she even said she slept with him and even tho we know that the kid isn't his we agreed to help her. I'm stuck in a ruff spot cuz she is only doing this because we found out I'm pregnant.

but of it is his we can get full custody due to the fact that I took a knife from her three times while I lived with her because she was trying to hurt herself. I need some help!!!!