I don't know what to think now

I've been trying to conceive for 4 years now and my boyfriend has low sperm count. So I been having sex with someone for 3 months. He's closer to my age and it's amazing. So we had an incident where the condom broke and he already came In it. He was freaking out. Oh btw he has no kids I have 2. So he's not ready to have children but he knows I want more kids even if we're not together. So I told him if my period doesn't come on I'll let him know. Buttt yesterday me and him had sex again and he came in me and im nervous. It's like I'll have the child I've been trying to have.. So is there women that ended up getting pregnant by someone else other than your spouse?

Update: yes he knows im cheating but can't prove anything. Hes okay with it I'm younger then him so he don't say anything to me and I dare him to