baby mama/spouses ex drama. what would you do?!

Jaelynne
I guess I'm turning to here because none of my friends or family understand what I'm going through so it's hard to talk to them about it. 
Ok so very long story short.. 
I met my husband in may- I was aware he had an ex girlfriend who was 3 months pregnant. (By ex girlfriend- they dated for a month and my husband was not happy with her but she did get pregnant). he tried to keep contact with her because he fully intended on being in the babies life. she ended up cutting ties with him when he left her, and had a new boyfriend be the child's father. (To add, she is not a good person. threatened abortions and miscarriages even faked going to an abortion appointment to try to keep my husband around) My husband didn't give up, he constantly asked to see the baby, offered money or things she needed for the baby- just to get turned down. She has even gone as far as to say she's glad I had a miscarriage because my husband doesn't deserve another child.  Yes, he should have gone to court a long time ago but he never did. She filed sole custody papers with lies that my husband was abusive (he wouldn't hurt a fly) and that he was a danger to the child. things got so out of control and things were said on both ends that it just became a toxic situation for everyone involved. my husband has yet to even meet his child who is now 15 months old.  The mother of the child has had at least 3 guys hat we know of (from seeing on social media) call her child their daughter/have the child call them dad. my husband doesn't even feel like the child's father from being pushed so far away. 
His final decision was to give all his rights away (he still plans on paying health insurance and child support like he always has, he just will stop reChing out to the mom) and wait until his daughter is old enough to understand things/wait until the mom has no control and then reach out to her. 
Part of me says it's the best thing to do for the child to not be in such a toxic and drama filled situation.. Part of me is sad she won't know her real father cause he's an amazing man. And we are trying for a baby, and I hate knowing my children will have a half sibling and not be able to know her. 
I guess I just need some input/opinions on what you would do or say.. What's right.