Need advise..

I'm not sure where to post this but I have a 5yr old and currently having issues with his bio father. He hasn't bothered to see him in 6 months and he does this all the time. He will go away for awhile and then come back randomly demanding my son. I'm trying to figure out how to keep him out of our lives because he only hurts my kiddo. He asks where his dad is or if he is actually his dad or if my husband is. My husband is a wonderful father to him but I fear with bio father coming back and forth it will cause my son to feel unwanted and that not only pisses me off but breaks my heart. Any of you ladies have advise? **not looking for legal advise, more just support and stories of how you handled the bio father and the questions my little boy keeps asking me.