@MoreLegsThanMe
Just seen your thread and read through all your posts. I'm so sorry you've been having to deal with all this and I can't imagine how fragile you feel right now. Well done for speaking to your GP and getting help with your state of mind - that's an incredibly brave thing to do, and reveals that you're strong enough to make those sensible decisions even whilst running on autopilot.
I don't have 5 children, but I do know what it's like to be left for another woman out of the blue when all you've been doing is helping your partner work through problems. It does feel like you've been used (even more so than usual), and it is a kicker, but one thing I want to tell you that took me a while to really understand is... that you aren't responsible for any of this.
People do change - and not always for the better. The man he is now is not the man you fell in love with, and that's not your fault. He's chosen to deal with his problems by running away into fantasy land with a woman who doesn't know all of his baggage, and by painting a happy fantasy life. That's a selfish, cruel and deluded coping strategy that he has chosen by himself.
Being left without warning is a huge shock to the system, and it will take you a while to adjust. You're very lovely, telling your DC that you're taking sides whilst wanting to howl into a pillow and instead, holding it together, but it's gratifying to know that your family are siding with you anyway.
Life is different. Some of life may feel worse, but some of it will feel better in time. I promise you, there will come a point when you feel like a whole person again, and when you can see things in your life that have improved for surviving this breakup. I know it's too soon to picture any of that and you're just making it through each day as it comes, but as a stranger looking in, I can tell you that there are better days ahead that I can see even if you're too upset to. They will come.
He's broken his relationship with his children, and with you. It really is his loss. You're doing so, so well, and you know what? You're magnificent. You are. You might not feel like a role model right now, but I'm in awe of your strength to keep plodding on, and so are the other women reading your posts. Never forget how amazing you are - remind yourself of that each day.
Take care, you incredible woman.