I read it on Ao3 for sure, plot goes like this more or less:
bruce agrees to get locked up, and Shield provides him with a small apartment, where no one ever visits and he goes slowly crazy, builds pillow fort, stops eating and then culson, clint and natasha (and a few times maria hill), start visiting him as a reward for good behavior (he has to start eating regulatory, ect.). natasha starts teaching him russian.
and then something happens and no one visits again and he starts going crazy and talking to his invisible friends again... and so on,
anyone? sound familiar? will provide my firstborn in reward for link to this story!
EDIT: as billiant melodyunity
pointed out its equally brillaint Running with Scissors