RMG, It sounds like you did all you could to make the marriage work. Some people do have more "staying" ability and the desire to make things work. I think it may be that some people are just less selfish and they are content to take what they have try to make the very best of it.
Glad to hear there were no children with XW#2 to add any more difficulty to the situation. Also, I'm glad you have found something good now, and I hope #3 is the "charm." I will try to catch up on your situation.
Arthur, I think oftentimes MLC starts prior to the larger changes you see. I know with my husband there was a general unhappiness which eventually led to self-absorbed teenage-like behavior. I think one of the reasons it may be difficult to spot is it is a gradual thing that can last quite a few years. I think that's why when you are "in it" it's difficult to realize and even admit to it.
There is no arriving, ever. It is all a continual becoming.