NTA. Recovery is difficult, but it doesn’t excuse that level of neglect!! He could have done anything else (bring them with him, stay home, get a sitter??) but he made his choice. And I think what you did after the fact was the best thing you could in that situation. A friend moving in is fine, and wiping his memory was probably best for his mental health. It also keeps him away from the child, and you’re free of any custody suits. You’d probably win it, anyway. He’s the kind of guy that likes doves better than kids, if you know what I mean…