Reminded me a little bit of...
...the 2004 film Dirty Filthy Love, starring Martin Sheen and Shirley Henderson.
IMDB link: http://www.imdb.com/title/tt0411291/
Does anyone know any more similar films? (preferably low budget or at least nothing that glamorises or trivialises mental illness)
EDIT: I'm actually making another suggestion before anyone else - Poppy Shakespeare (2008), http://www.imdb.com/title/tt1106448/