"Ask yourself, 'What is it costing me to be in this relationship?' If the answer is your dreams, identity or dignity, the cost is too high." -- Dr. Phil
Yeah, I just quoted Dr. Phil.
Here's another sentiment along the same lines. Someone asked James Altucher "When is it time to leave?" (You know, if you're even asking, something's not right.) He says, "have the arguments worn you down to the bone? That's when it's time to leave."
And a third thing, along the lines of things that wreck relationships: an article on the 4 easiest ways to accidentally ruin your relationship -- from Cracked, so it's funny as hell -- but also true.
I don't have any fight left in me anymore.