While I suspect that MLCers need to hit bottom to come out of it, many do not, and it isn't only other people enabling them. Many MLCers seem to get stuck in victim mentality mode. They see others as rejecting them, even though they actually did the abandoning. They remain stuck in misery without the tools or the will to sort themselves out.
I think this is the hardest part for the spouse, seeing someone who is not going to get better. In a bad way, but not bad enough to prompt them to do something.