My man got his one night stand pregnant while we seperated. And I was already pregnant

Ok so I'm in a situation here. Ok let me tell you. I've been in a relationship for 2 years now. I got pregnant 6 months into our relationship. I have a 4 year old that my boyfriend has been taking care of loves her like no other. But anyways. When I was 5 months pregnant we ended up separating for a few weeks and I left back to my hometown. We still talked planned on getting back together but we still on the rocks.. ok so he has a one night stand and the girl gets fu kin pregnant. I end up moving back in with him after we decided we needed to be together. And after a week or so this girl messages him that she's pregnant and wants him no where around or help because she could handle it and yeah. We now have a 6 month old and child support papers came in the mail for him.. ugh I'm already going through post pardum depression and staying home alone with the kids... :/ idk what to think or do. I love him so dmn much and we've been through a lot to just throw down the drain. Would you be able to forgive him??? I need help bad