Question, were they toxic while in a relationship or did the relationship help to grow them both for the better?
There are cases of depressed people seeking an ex relationship for comfort, even if it's a bad one though, I'm just suggesting.
@LuoirM as much as I hate replying to you. It was her that wanted to go back together, she's kinda the one wearing the pants in the relationship before.
Understandable, hope the dude gets well then. I lost contact with someone like that once and still thinkin', occasionally ask him out for pho or sum.