If you want to go "on record" as standing for the marriage, it may be best to do it in writing. Words can be easily forgotten or twisted around at a later date.
Puppy Dog, you make an excellent point about truth darts. I used to throw those out every once in awhile. But I tried to be very careful how I worded them. If my husband felt I was blaming him, he'd get very defensive and would have found it much easier to run away rather than turn around and try to work on things. He would have seen me as the evil witch pointing out all his negatives.
Instead of telling him how he was hurting the kids, I might share with him an example of how much they missed him. For example, there was a comic in one of the Calvin & Hobbes books I read to my son, and it showed the dad reading to his son and there was something about how nice it was to have his father reading to him every night.... when I read it to my son it made us both feel really sad. I relayed this to my husband and I could tell that dart made a definite hit.
Another thing, rather and focus on the "marriage," and my husband's relationship with me (which he was only seeing in a negative light anyway... OW just looked sooo much better!), I focused more on him losing his "family," and not being part of all the fun things the kids and I were doing together. I might throw a dart out about how his kids missed not having him there. Once I remember sharing with him a place we visited and how sad it was seeing these other families together with moms and dads, and how we all felt a little sad about him not being there with us. I know it made him have a little stab of regret that he was not there either. I think it also made him look more at intact families when he took the kids out too, and he recognized and felt that same experience too... another little dart that hit it's target!!!
These are only suggestions. Your husband may be much different from mine. But every time you say or do something look at the results. Did it bring him closer to you and the family, or did it push him further away? Whatever pushes him away, don't do it... whatever seems to pull him closer... repeat.
There is no arriving, ever. It is all a continual becoming.