Adopting and expecting 😱

I was born and raised in detroit and moved to Florida in 2010. Shortly after my childhood best friend since the age of six turned into a very bad drug addict. I have kept close contact with her and her family over the years. She already has it that was born with cerebral palsy that her aunt raises. I found out a few months ago that she was pregnant and have been keeping very close contact with her family during this time. I got a phone call from her niece saying that she had the baby. When she was released from the hospital the baby stayed and I finally spoke to her after more than a year. I asked her if she would like me to adopt her baby and she said yes . I flew out the next day no questions asked and went to see her yesterday. She is the absolute epitome of beautiful and as a mother of four boys I instantly fell in love when I saw her. Financially, emotionally I am ready but The only problem I have is my fiancé is not as thrilled as I am being that we just found out I'm October 26 that I was pregnant. My fiancé was adopted as a child because his mother was raped  at 16 and she gave him up, I want The baby he really doesn't. I have begged and pleaded with him and explained my connection with the mother of the baby to try to get a better understanding of where it is that I'm coming from. I don't want to give him an ultimatum and ruin my family but I also can't bear to leave this baby in Detroit knowing who she might go to... What can I say to make him better understand?