Clint is injured on a mission (I'm tempted to say he's paralysed but it might be something else) and can no longer go on missions. His prospects of recovery are very low or nonexistent. Clint becomes very depressed and finally tries to kill himself by jumping off the Avengers tower but one of the other Avengers manages to catch him (might have been Bruce). The Avengers all live at the tower together. In the end Tony finds a way to fix him and he returns to duty.
It's a long fic, I'm thinkin at least 20 000 words, probably more like 30 000 (but again, I might remember it wrong).
Ring a bell, anyone?
Found: If the Night Runs Over by NiennaNir