Adult or not, IMO it's not healthy for her to keep a relationship with this man or his family, especially if she sees him as a father figure. She saw him one way, but that's not how he really is if he's still actively in addiction. "He was the fun one who'd do anything for her" but this was a mask. She'll likely see through the veil eventually and end up very hurt or disappointed. The fact he's reaching out to her seems like a real boundary violation as well.