Hello and welcome
I was brought up by my step mum, as my birth mum didn't want anything to do with me. As far as I'm concerned, genes don't come into parenting. Your boyfriend sounds like a wonderful man, and the father of your baby. The other guy doesn't deserve a second of your time in my opinion. I hope that doesn't sound nasty.
Sorry to hear you're having such a hard time, how long do you have left?
xxx