Help! My fiance may be the father of two other children, I need advice.

My Fiance and I have been together 2 and a half years, we have had out ups and downs like every relationship. Back in September he and I broke up for 2 weeks and he fell off the wagon and smoked meth for the entire length of time he was gone. He said while he was high he slept with someone at work and about 9-11 days later she finds out she is pregnant and says she doesn't really think he is the father but can't be a 100% sure. Okay he and I got back together and I forgave him for that and excepted that he may be the father of that one. He has since been clean and changed jobs now that he is back home and continuously tells me he is sorry for what he did even tho we weren't together at the time. We'll I am currently 11 weeks pregnant with our child and we get a call today that a lil boy who is two could also be his. We talked to the mother and found out she got pregnant the month before my Fiance and I meet. He says he doesn't know if he is or not because the woman slept with his brother and someone else around the same time, she says otherwise. I dont know what to do guys I'm extremely upset and just want to cry my eyes out. He is mad at me because I am mad at the situation and says I have no right to be angry because it was before we even meet. I tried to explain to him that im mad because I didn't sign up for this I knew of the 2 kids he has with his ex wife and I accepted them but I dont know how to feel or think about the whole situation. What would y'all do if you were in my situation. Also it goes to say that I did tell him I would leave him if the baby the other woman is currently carrying turns out to be his bc I am not going to live with having to constantly see her and deal with the fact she knew he and I were together and then broke up and even said she knew he would go back to me. I feel as if she was just waiting for the right moment to swoop in.