What a strange film. I swear I'm not sure how I feel about it. Well, this is a rough idea of what you'd be in for if you view it. A careful, nearly meticulous look at two functioning people with specific psychological issues. If it's a dark comedy -- I didn't quite get the humor, though it does have some humor.
More it seemed a commentary on how those with serious issues find a way to make themselves happy, not by working out their issues, but by working with them. If this is the case, then this commentary isn't very inspirational, at best bittersweet. Two dysfunctional people fall in a twisted sort of love with each other, mostly via a twisted sort of sexual attraction.
They find a way to meet each other's needs in a way that is both abusive and yet satisfying. Perhaps it's an exaggeration of what real couples do. Though our neurosis and quirky needs aren't quite as unacceptable as the two in this film, perhaps the common couple is guilty of the same sort of generalization. Instead of doing the hard thing and working out their problems, the common couple finds a way to spite each other just enough to feel/fake pride and independence while not so much as to send the other running away.
It's not a pleasant thought, but maybe a wake up call. Be forewarned this film gets pretty sadistic and displays the sexual in ways that will no doubt be offensive to many people.