I think it started out with her just getting comfortable and lazy as fuck, then she gained the way and her laziness took a real toll on the relationship and she became depressed.
I know she's depressed now, but I'm having a hard time feeling sorry for her because at least from what she's told me, she brought it on herself by putting her marriage ok the fast track to shitsville...because she even said when she started doing less and less her husband was still fighting to keep things good and doing a lot for her and she was still doing nothing back.