R.,
Hello. You're in a tough situation as the Mom. I would say your son NEEDS to do this for his own knowing.
I'm coming from a stand-point where I was a child and wanted to meet my bio father. He made a choice to leave his wife (my Mom) and newborn baby (I was one week old). We had no contact while I was growing up, but I was a very curious child especially as a teenager to meet him. I wrote a letter to him (that he claimed he never received), but he called my Mom just a few months later to try to contact me (when I was 17). We had dialogue over a few letters at first, then I had phone calls with my half-brothers, then there was a meeting. He lived in a different state, so my uncle went with me. I would say here are my lessons learned:
1) Let the contact be child driven (since he is old enough) - that could be a letter (and that’s enough) or eventually maybe a face-to-face meeting. But, let your son guide what he wants out of this and at his own pace.
2) If they have a face-to-face meeting: Only expectation should be to actually meet him. I always thought my first question would be "why", but once I got around my father, it was so clear to me that it didn't matter "why", by his leaving I was given such a better life (but it took me meeting him to realize this). Other more insightful questions came to me in the moment to learn about him and who he was and that told me mostly what I needed to know. He was the first to provide excuses for his leaving, but in the end it didn't really matter. I had the best family (without him).
3) Let your son ask his questions, even if it's "why where you that way 20 years ago". But, know that it's up to your son to either trust his answers or not. And to be honest, the bio father may not know “why” – or if he gives reasons, they may not be very good. But, if that’s what your son is seeking, he should be allowed to ask it. I had to realize that no matter what the excuses were, we all make choices and even though that choice had hurt me for years, I realized I had been given a terrific life and at that point I was so thankful for his choice of leaving and my Mom's choice of requesting his rights to be taken away.
4) If they have a face-to-face meeting: Have an adult support person there with him that he trusts (like an aunt, uncle or close family friend - this person has to have a calm attitude and isn't upset with the bio father), I think it would be hard to have you there at the first meeting. This person helps mediate or stop things if they were to get too upsetting (they have the best interest of your son at hand). And this person is a good person to talk about those mixed emotions they might have, a good listener (that’s not intimately involved).
5) If they choose to continue contact after a face-to-face meeting again, let it be at your son's pace. Personally, after some more contact, I didn’t want all the drama that came with my bio father, so I ended contact. But, meeting him helped me fill a huge desire of the unknown (just who he was), and it helped me see how wonderful my family was and helped me to understand why my Mom did some of the things she did (that I had been upset with her over for years). As hard as it was on my Mom for her to let me meet my bio father, it was a great gift to me and gave me a great appreciation of my “true” family (just at 17).
6) You also might seek counseling too, it's a place where your son can safely express his feelings (no matter what they are in the moment - good, bad, indifferent). I had good counseling prior to meeting my father; I think that’s why I was able to take it all in from a different perspective. Had I not had that, I think I could have been highly disappointed and/or taken in easily by his excuses. And it’s potentially an emotionally draining process (even when it’s good). It would be a good sounding board for your son, would still encourage him to go a few times prior to meeting bio father and a few more times after initial contact (it's not a life long thing, just during this major life event). If he still won't go, I suggest you attend to help you work through your emotions (my Mom did as well).
There’s not a right or wrong answer here, some people have no desire to meet bio parents, while others long for it. My main piece of advice for you and your son is don’t have too many expectations (the bio father has been known to let people down before).
Best of luck to you and your son.
~ J.
P.S. Prior to meeting my bio father, I had a fantasy image of him and how life must be in his household (the unknown plays tricks on us and it was an easy escape as well when I was upset with anything in life). Meeting him and his other children, I found out he was an extreme alcoholic, physically abusive, a liar, and so much more. That fantasy image quickly faded, but it helped me realize I already had the ideal family I really wanted, just had to see the other side to realize it and the not knowing would have probably always made me resentful to my Mom for some excellent choices she made (once I saw the truth). It wouldn't have had the same impact had she just told me (she voiced a few concerns and shared a few situations, but said she hoped he had changed for my sake), still I had to find out myself (stories from his family, but I wanted a clean start, and he began to brake promises and only gave excuses for everything). I'm still glad I went through this process; I HAD too for my own peace. Just wanted to add that piece to help you realize that what your son feels in normal and he really does need to do this. I hope it's a good experience and that he truly evaluates what's being said and he'll eventually sort it all out. Believe in your son (not the bio father).