I don't have advice for you, exactly... I just thought I'd tell you about my experience.
When I was young I asked about my biological father a lot, and wanted to meet him. My mother was honest about how her relationship with him had basically been a one week affair. She was still in contact with him even though he lived in another state, because she felt he should know about his child, but he didn't want to meet me. I had all kinds of fantasies about how wonderful he would be, how happy I would be to meet him, and how our lives would have been so much better if my parents had stayed together. I wrote letters to him asking him to come see us. I think it is probably normal for kids to wonder and fantasize like this about the absent parent.
Then he suddenly wanted to meet us, and came to visit us. I think I was 11 at the time. Of course, he was a total stranger to me. He came up to me and suddenly grabbed me and hugged me (while I was trying to escape) and told me he loved me. Imagine, a strange older man doing that. It was horrible and creepy!!
Anyway, it is now 30 years later and I still don't feel any connection with this man. I think by the time we finally met, it was just too late for me to feel as though he were part of the family. We have nothing in common except genetics. I think of him as "the sperm donor." Unfortunately, as I have gotten older, he has wanted to play a "father" role more and more. He came to my college graduation and my wedding even though he wasn't welcome. He calls me at odd hours, wants to know about my life and then tells me if he "approves" of my choices in life (as though it matters to me). He insists on visiting from time to time, and whenever he visits, he always grabs me against my will and hugs me (he is really tall and I am very small) and it is SO creepy for me. In the past I have tried to cut him out of my life entirely, but other relatives always make me feel guilty about doing that because he is my "father."
It's easy for me to wish I had never met him and he had just remained an abstract "sperm donor"... On the other hand, if my mother had hidden him from me, I probably would have continued to fantasize about how wonderful it would have been to meet him, I would have been angry at my mother for hiding the information, and it would have been a big issue for me. So I guess it is better that she was honest and open, even though it means that I have to put up with an extremely irritating relationship with him as an adult.
Edited to add: We didn't have another father figure around when I was a kid, either. But my mother had several close female friends, who were a big part of my life, and are all still very close to this day. I'm very happy about that. One's family doesn't have to consist of "father" and "mother" to be close and loving and supportive.