I read this to be that there is a known birth father from a previous relationship before the marriage. That his ex-wife had a child going in.
“My fiance was married for almost 8 years. His, at the time, wife had a child from another man. While they were married, they began to explore the process of adopting said son. They decided it wasn’t necessary for the price.”
If after “another man” there was a comma and a period after “while they were married” I would have read it the way you are reading it. And I see it now. Or if the sentence started with “At the time, his wife . . .”
So I did not even go into 7611 presumed father stuff like:
(c) After the child’s birth, he and the child’s natural mother have married, or attempted to marry, each other by a marriage solemnized in apparent compliance with law, although the attempted marriage is or could be declared invalid, and either of the following is true: (1) With his consent, he is named as the child’s father on the child’s birth certificate. (2) He is obligated to support the child under a written voluntary promise or by court order. (d) He receives the child into his home and openly holds out the child as his natural child. (e) If the child was born and resides in a nation with which the United States engages in an Orderly Departure Program or successor program, he acknowledges that he is the child’s father in a declaration under penalty of perjury, as specified in Section 2015.5 of the Code of Civil Procedure. This subdivision shall remain in effect only until January 1, 1997, and on that date shall become inoperative. (f) The child is in utero after the death of the decedent and the conditions set forth in Section 249.5 of the Probate Code are satisfied.
I read the question to be that the child was there before he got there, (not that she had a child from another man during the marriage) hence there was a different father. The presumed father analysis from 7611 did not even get there.
I can’t tell from the question if birth dad paid support, sent cards, visited, etc. If she had the child from another man during the marriage my answer would have been different.
I could add as a new paragraph 3:
After a further reading, your question is a bit unclear. If the child was born during his marriage to the previous spouse, your fiance will likely be the presumed father of that child, assuming that the biological father is not in the picture visiting, paying support, etc. He will not need to do an adoption at all . . . the Court in his family law case will presume that it is his child, and the Court will determine custody, visitation and child support issues.