Wow TF. I am so sorry all of that happened. I got teary just reading it. Sitting through it and watching you daughter go thought it must have been excruciating. Sounds like you handled it as best you could though and that you have a good plan about how to manage her feelings. So unfair. I live in dread of eventually having that conversation with my 10 year-olds. Even though their dad is currently living elsewhere, I don't think it has even occurred to them that this could be a permanent situation. They are used to him not being around and he has actually been more available to them than he was when he lived with us so things haven't been too bad. But if we were to ever tell them this is going to be permanent...that, I know, would hit them really hard. I just pray we never get there. But if we do, I will think of your good example and try to give the same message. Really tough to say it is "our" decision when you know darn well it is not. But...it is better for the kids to not blame one parent if possible.
I totally get your fears and negative thoughts. You wouldn't be human if you didn't have them. I don't currently have another person to focus on in my sitch (not sure if you do or not as I haven't read you entire thread) but I will not go anywhere near the place his is living. He had been going there three months before I found out about it so to me, it is his OW. I've been there once and it made me physically ill. I will not go there again unless it is to help him move his stuff out. Anyway...try to replace those bad thoughts with more positive, realistic thoughts. "I don't want my kids to call another man Daddy" to "Even if my W finds someone, there is no one, and I mean no one, who can even come close to being their Daddy other than me." That is much more realistic. Guaranteed. Your worst fears are just thoughts created by you and nothing more. Keep moving forward. No fear... (((HUGS)))