Well you tried and your the better one for taking him back and trying to make it work, he on the other hand is just a coward. He'll realise one day what he as lost and walked out on and soon the kids are going to make up thier own minds as they are getting older. And he won't like the outcome of that.
Ive been following your thread and i think you are are great woman, i think you are brave and strong and will put your kids first and above everything.
Leave him to live his sad little life with her, they make a great couple and will never acheive what you have...... being the best parent ever.
I wish you the best of luck with everything you do and when the time is right theirs always someone out there for everyone, and you will realise why on earth you spent all your time with him......lol.