Double baby daddy

I was with my partner for four years and for two of those we were ttc, but after two miscarriages and an endless amount of negative tests our relationship broke down and we decided to end it. Since then I have been seeing a guy I had a thing with before for my ex for about three months now. We always had strong feeling for each other but the time was never right and I used to live quite far away. I'm pregnant, 8 weeks so still early but everything I've ever wanted. It was a shock though as I'm so used to negative after negative and it wasn't even planned this time. He told me that he would support me no matter what I wanted to do but as I was keeping it he wanted us to be together to raise the baby. But his ex-girlfriend is also pregnant and due this month. Their relationship broke down following them having a still born before this pregnancy, they decided mutually not to try again yet but she admitted she had been putting holes in the condoms they were using. She still wants to get back with him which is totally understandable especially since she's having their child. I just don't know what to do. He's told me that he's not in love with her anymore but will be there for the baby. I obviously have no issues with this. I'm just worried that when their child arrives he will leave and want to play happy families with her. The main thing I've wanted for my children is to have a stable family as it was something I've never had. 
What should I do, please help, my mind is on overdrive