Lots of people do get into relationships that require way more work to hold together than it seems like is healthy for anyone. I'm as guilty of this as anyone else: I've had my ultimatum-issuing moments; my moments of pretending everything's okay for the sake of keeping the peace ; my moments of silently weeping in bed, waiting for someone to fall asleep, pretending that not talking about it can make the problems go away and that just trying harder will make us not-unhappy and that not being miserable is a step along the path back to happiness. Commitment is important, right?
And, sometimes, I suppose, it can be. But other times — many other times — the betrayal is too great and the emotions are too dark and the road ahead doesn't go back to being nicely paved, but turns into gravel, then dirt and then mud.