Everything I've read has been recommended, in terms of self-help, but for one book, The Power of Now, which I'm reading now and while it's a little spacey in parts, it does talk about being in the present all the time.
This is a weird recommendation but I also read Rachel Hadas's Strange Relation, which is a book about her losing her husband to dementia. Honestly I think any book about grief or loss helps. I am reading John Banville's novel The Sea right now (fictional but whatever) about a character's dealing with the death of his wife. I think many of us dealing with an ex with MLC deal with the emotions commonly experienced by someone who has lost a spouse through death, as the "death" of our partners who seem to change irrevocably is like the physical death of a spouse. So I think any book about loss is helpful...
M45 Bomb 6/09; EA 6/10; Divorced 1/11 Proud single mom of 7 little feline girls and one little feline boy "Fall down 53 times. Get up 54." -- Zen saying
