Sorry I have been out for a few days. Very, very busy. Working a lot too.
Don't beat yourself down, it is not easy to deal with all of this, specially when you get so many mixed messages.
I would advise you to also read some of the stuff about MLC - mid life crises. I am not very sure if this is the case, but your Fiance is on that crazy age.
I think you are taking the right path for yourself. And you have recognized the YO YO effect much better then I did. I fell for my XWH's appeals many times, in hope that he was changing his mind to just find out he was not.
Today, I am more detached, and I actually feel much better, my heart does not hurt all the time, I have more peace inside of me and have more fun too.
Sometimes, we can't resolve other people's problems. Now, be aware that your feelings will also be up and down all the time. You take a good decision on day and feel miserable the next. It is pretty normal.
Hope you are trying the techniques from DB, they work for many people. It's worth to try because it is not only to rescue your R, but to rescue you.
Be strong, happy, better, fake it until you believe it. Your Fiance needs to know that you are doing well without him. Have some GAL, no talks about OW. Be unavailable, mysterious, have fun with your kids.
Leave him to resolve his issues. He can't blame you for things you are not doing. I would also encourage you to read some of the stuff in MLC - mid life crises. I am not sure if you fiance is an MLCear or not. But he is there on that age.
You said he has childhood problems, and it is amaziing how this stuff affect a person at that age.
Hope you have some plans for XMas with your kiddos. They deserve to be happy and you can make it.