I remember a lot about this fanfic because I read the book it's based on too, and not knowing the name of the book is killing me. The fic is basically the book with the names and genders changed; the book in question is a YA novel from either the 80s or early 90s about a girl who either cuts or attempted suicide. Her parents are constantly trying to keep straight razors from her-- I read the book in the early 2000s and straight razors were a touch outdated, so I remember that since I didn't know what it was! I think she has a little brother and maybe a stepmother(?) and a father? They don't quite know what to do with her. She goes to see a therapist regularly and sort of becomes friends with him, and falls in love with a boy she meets as she walks around the park who turns out to do landscape work. She uses running as a method of becoming healthy, but not more than five miles in one day since that would make her a health freak, or something to that effect. There was a scene where they were buying the shoes for her to run, which was encouraging since she was showing interest in something again. I can't remember what caused the suicide attempt. It ends with her therapy sessions ending, and she's sort of friends with her therapist. I think she might be going off to college at the end, though I'm not sure. I think Heero is the girl and Duo is the landscaping boy, but I might be reversing the roles. I think the fic was released sometime in the early 2000s (probably around 2004 or 2005, I think), so it was a while ago.
EDIT- The book is Life Without Friends by Ellen Emerson White, but I still can't find an active link for the fic; maybe there isn't one. The Wayback Machine finds it in the early 2000s with this link. The fic is Life Without Friends by Maxwell's Demon.