Adoption and calling him Dad

I’m a 42F with a 4.5 year old boy. Met an amazing man about my age and he wants to take on me and the child that is not his. The sperm donor of the child is gone and hasn’t made any attempt to try to be in the child’s life.

My question is twofold :

“Call me Dad” : This guy really wants to be a dad and have a child call him such. I understand his side of the fence, but I also think that it should come organically. For those who have been in the situation before, what do you do? Do you prompt the child to call him Dad or do you let it come on its own?

Adoption : The guy is also willing to adopt my child. The similar feeling goes to calling him, Dad. I understand his side of the fence and since there’s nobody else on the birth certificate, it would be fairly easy to let him take him on. However, I think it would be more meaningful if it came from my child.

From people who have been there before or been part of a family that has a similar situation - what do you do?