He didn't tell me he was infertile

I have cohabited with Brian for five years and we started trying to have children after the first year of our relationship in vain.

Since most times women are blamed for infertility, I visited different fertility doctors who told me that I was normal and I will get a baby eventually. Brian would also tell me to relax, promising never to leave me for not conceiving which made me relax.

However, he recently travelled for a two months business trip and I found myself cheating on him with another man and conceived.

When he came back, I succeed luring him into having sex with me and after two weeks I tried telling him that I might have conceived.

To my surprise, he interjected immediately saying that it is impossible because he is sterile. That he had feared to tell me thinking would leave him.

I felt so betrayed and the guilty I felt for having cheated on him stopped.

However, my child's father is poor and I still love Brian.

How do I keep my baby and stay in my marriage?