Loneliness or loners, misfits, etc?
Guess there are pretty famous ones like Lost in Translation, Taxi Driver, The Coversation (ish), The Machinist, etc.
Particularly looking for something where you feel proper empathy for the lead character, Y'KNOW. My two favorite films of this ilk are Garage, an Irish film about a sort of village idiot type, and The Wrestler. Guess some of Shane Meadows films are a bit like this.