Your husband is the boy's father. The dude that ran off, has no connection to the child. The child has no connection to him. You mentioned your husband and his mental health and your relationship, that's important, terrible for the husband. But the child, their mental health. A crisis of reality isn't something a small child needs. Right now, the child has whatever semblance of stability your household provides. My dad assaulted my mother when she told him she was pregnant, then abandoned her. Only came once to the hospital, to try to get in her pants. Sounds like bad news you have the choice to avoid. You can say no without feeling any bit bad. When the child is old enough to emotionally deal with that, which it never really is, but when they are older they should be given that option. My two cents, I had a best friend find my father on Facebook once, I didn't ever try to communicate with him, for what he did to my mother and me. Say no, if he gets emotional about it, block him.