BE you. Don't worry about being anything, or anyone, else.
I know you are worried about the kids. And I know it will be hard for them. But a lot of how it is for them is going to come from how it is for you. They will follow your example. If you are confident that things will be ok for them, they will be, too!
I was worried to death about telling our kids, especially the younger two, S11 and S14. But in truth, and I am not making this up, they have been better from the day we told them. They knew something was up, for sure. But the reduction in tension when we told them was incredible. Is it the ideal? Of course not! Does it have to ruin their lives? NO!!!!!
I don't know what to expect in mediation, but my advice would be to let the mediator handle the confrontation, while you listen, and work towards a fair deal. H is most likely going to propose some things that don't make any sense to you. Try not to get angry... it probably makes sense to him! Let the mediator steer him away from that stuff, I expect they've heard it all!
As far as guys, and making up their minds... I don't know. I think the hard part in getting them to "come back", men or women, is their pride. It's definitely a hard nut to crack. All you can do is make what you can control safe for him. After that it is up to him.
