He got another girl pregnant...

We have been on and off for 3 years. And we had broke up for a couple weeks and during this time he went out and had sex with another girl. Long story short the condom ended up breaking and now she’s pregnant. We are currently back together and now engaged. We were ttc 4 months before we broke up and I still haven’t got pregnant. Am I wrong for being jealous bc she gave him a baby and I couldn’t? I feel so worthless to him bc I couldn’t give him a baby. He is choosing to stay with me but we are going to try for full custody as she is a very unfit mother. He wants me to adopt his baby with her, which I have no problem doing. I just want my own baby as well and as of now we are currently trying but I feel like it’s not good enough.