I never want to be right about this kind of stuff. I always think of the most selfish, self-centered, jerky thing, and assume the WAS will think that way. Then I am glad to be wrong.
You missed my point about him always taking vacation on your anniv. He took off the first year because it was your anniv. Maybe he even thought of it himself. After that he took off because you had a good time the first year, and so a tradition was born.
Now he does not want to celebrate your anniversary because he does not want to honor your marriage. How can he, after all he has done to ruin it? He is at least showing a little integrity by not trying to pretend everything is normal for one day a year.
Figure out which days you need him to watch the kids. Ask him to put in for vacation for those days. You don't have to tell him why those days--he isn't stupid. Tell him you're going to Vegas if you want, or not. If it comes down to it and he wants to come along, I'm sure your MIL will be thrilled to watch the little ones for the 2 of you. If not, you'll be in Vegas and he will be with his little ones at his mom's (not with OW) on your anniv. I'd love to know what he thinks about that day.
