As desolately lonely as it is to be by yourself, it is a scorching, soul-withering hell to be in a bad relationship and effectively miserable and alone. The really bad relationships with bad people are difficult to get out of if you've been together a long time. The really bad relationships with good but profoundly mixed-up people are even harder to leave.
I spent a huge portion of the last twelve months getting extricated from a serious three-year relationship with a wonderful person who'd somehow managed to get herself completely stuck in life. I still care a great deal for her, but I wouldn't go back. It's lousy being by yourself, and when the apartment's a shambles, and the money's run out ten days before payday, there's nobody to yell at besides yourself. But it's a twenty-four carat delight to know that, though you've got lots of problems, dealing with somebody else's problems isn't one of them.