The child father do not want this child he want to give it to the birth mom relative do he still pay support

If the relative wishes to legally adopt the child then he can relinquish his rights as part of the adoption process. In that case, when the adoption is final, he will not longer be responsible for support.

He's the dad.. he's going to pay support for at least the next 18 years...

No way he's going to get out of it unless the mothers next husband wants to adopt it, or someone else does.

That's how it is... there are no papers you can get from Walmart you can sign that changes it... kids aren't possession's with titles like a car... or a pet.

Your post is a bit unclear.

Does the mother of the child also want to place the child up for adoption, or is it just the father that wants to give this child to a relative?

If the mother of this child does not want to place the child up for adoption, then no, he can't give up his rights, and yes, he will have to pay support, even if he doesn't want to see or be a part of the life he helped create.

If the mother agrees to the adoption, then both biological parents would give up their rights to that child to make way for the adoption to go forth.

Unless there is an adoption, he can not "give his child away, this is not a puppy dog.
So he will need to pay child support according to court order, to who ever has legal custody of the child.