Only if you can PROVE he is a danger to the child can you strip his rights from him.
If your fiance wants to adopt, here's what you should do:
1. GET MARRIED. If YOU aren't willing to make a legal, lifetime commitment to someone, why would the courts see a reason to award a legal, lifetime commitment to that person for your child?
2. Get a lawyer. You CAN do adoption without a lawyer, but you can also set a bone without a doctor. I wouldn't recommend either.
3. ASK the biological father if he'd be willing to sign over his rights. If he will--there's no problem and you move forward with the adoption. If he will NOT--well, start getting that child support order enforced. If you do not HAVE a child support order, he owes you and the child NOTHING. So GET an order, or let him know that you will be pursuing child support if he doesn't sign over his rights.
4. Go to court for the adoption.