My boyfriend wants a divorce, but I don't want him to get one.

Yes you read that correctly. I have been in a relationship with my boyfriend for 3 1/2years. We have been together off and on for 19 years. 3 years ago he got married. She knew that me and him were together at the time. She wanted 3somes I did not. So me and her don't talk Anymore. She doesn't know that me and him have been together off and on for the past 19 years. (She and him got together 18 years ago.) She also doesn't know that he got me pregnant 19 years ago. I lost the baby. I tried breaking up with him on several occasions. But he is kinda crazy and stated he wouldn't let me move on with someone else. Well I am pregnant now and he is talking about getting a divorce. He wants to move in and marry me and raise our son together. I don't want to be in a full time relationship with him as I only like having sex with him. But I can't really break up with him because we are going to have a baby. I don't know what to do. Abortion is not an option. And I wouldn't risk her harming my baby by giving it to him.I know I'm going to get crap for this but y'all have to understand they both pursued me. She became upset because I'm not into women. Plus she married him knowing that he was with me and that he didn't really want to marry her.

Edit: My ob/gyn told me 12 years ago that I would not be able to have anymore children.

He and his wife no longer have 3somes or sex with each other, at least that is what they both tell me. I believe thats what i am for as I only think she wants to be married not have sex. ( he is controlling and made her participate in 3somes. She says she never really wanted to)

Me and him first started hooking up in 2001. I didn't want to be in a relationship with him ( even though he is handsome and a good provider and good in bed. He is also controlling and has anger issues) so he got with her in 2002. I would hook up with him whenever I wanted to. She didn't know then. In 2016 me and him started"dating" full time with her knowledge. He has told her he only married her because they have a child together In front of me. (their child is now 17 and he feels she is raised now).Which is why I believe he wants to divorce and marry me. But I don't want to be married period. And definitely not to him. Because I only want him for sex. ( I have expressed this to him many times before And during my pregnancy.) I like being by myself and don't want a traditional relationship anymore just sex.