I also vote for talking with your son, and following his wishes (unless he wants you to lie to them). Probably the less involvement you can have between them all the better (for you).
I've been in contact with my birthmother, but have never met her. I'm SO thankful she isn't close in proximity to me as I read this. I never thought about reaching out to her in my teenage years, however, but did later when I became a parent. I sense she has her own bag of issues, and am not sure if I want to take a peek inside of it.
I can't believe his bio-mom lied to you about his whereabouts. Highly concerning.
I'm sorry for the pain you're going through with your son.
