I imagine even if he 'knew' about her past/backstory he'd still prolly feel awkward and keep his distance even if he never tells anyone what happened
Maybe for people who isolated themselve from outside world or somehow don't know about people having issues.
Personally, I know people like that do exist, heck was in relationship with one, gave a whole lot of TLC, understanding, we went to the professional even a couple times which helped a bit.
Sadly things went south after about three years, hiding her issues and succumbing back to alcohol addiction in secrecy, we tried rehab, it was successful but other issues came out and unfortunately we had to break up...
It's a hard "work" and takes a lot to help such people, there's probably no way to "fix" someone like that, especially if there's little to no effort when a person is depressed. But doesn't hurt to try...