I shall keep you in my prayers for healing and comfort and wish you great success in future.
Elliott, MAE, LPCC, NCC, CCMHC
If you want to have some mental understanding of what's probably going on with your exhusband, I can offer that. I wonder when you first met and fell in love? how long you were together before marrying? and how long you were married? and what the problems were that led him to leave you? Or did he just "fall out of love with you" to phrase it the way he may have explained himself? And did you have children together?
Now this is what my knowledge of love in the brain suggests: IF you were each other's first great loves, that is fully committed love of more than 2 years, but probably more like 4 to 10 years, then you both formed complex neuronal networks of "love-partner" in your brains, including the cerebellum, where probably our unconscious mother-complex and father-complex, and (new concept) partner-complex are centered. So, when he chickened out on dealing with the not-so-easy knotty problems of adult married life (one such problem for a man happens when his wife devotes more of her passionate intensity to her infant and has less time and passion left for her husband, who was used to being the center of her universe until then), he "naturally" (that is unconsciously) sought out a person who either looked or acted a lot like you, so she felt right to his internal partner-complex of you. So he is in effect trying to START OVER with his love for you, but with a "blank slate" so whatever the "bad" (= difficult to cope with without growing new capabilities in himself) things on his mental/emotional memory-bank of you aren't there (yet).
The bad news (for him) is that she will turn out NOT to be you, and those differences might start bothering him as much or more than the problems he had in dealing with your marriage, AND she might realize that he's trying to make her into somebody she's not, and their marriage could crash even sooner than yours did.
It always feels worse to get left than it does to initiate the leaving, because you're helpless to bring him back. But the chances are very good that his primitive attempt to wipe the slate of his marital problems clean and start over will come back to bite him for longer than your grief is hurting you now, and he will get both a compounded confusion inside, because he was trying to duplicate his early relationship with you (which happened to me) and she will outgrow her romantic idealization of him even if she never realizes that it's not her real personality that he's habituated to loving.
I do agree with the title of what Elliott suggested as a book for you to read. Because you can take the time (probably some years) of your singlehood to grow yourself a more independent and mature single personality, and have some healing love relationships that show you that what your ex couldn't appreciate (or couldn't cope with) other men can appreciate. And you can also engage in psychotherapy, which is a Platonic love relationship with a teacher whose individual tutoring aims to help you discover and develop the unique individual you can continue becoming for the rest of your life. That psychotherapist (male or female, but Platonic love relationship) will also become an internal image with a core of wisdom and self-love.
I also have a 20 page appendix to my textbook Love & Intimate Relationships: Journeys of the Heart, called Breaking up with Dignity and Recovering from the Loss of a Love that I can send as PDF attachments, but I can't combine it into one file so it won't work to attach on this website. Nobody can transmit an email address here with the "at" symbol. But my research article on the internet Low Dose Naltrexone for Disease Prevention has my address at the bottom of p1. I haven't read the book Elliott's recommending, but what I know about healing relationships and a few other dimensions of post-breakup issues and communication may still be largely unknown in the popular books.