Hi dejavu, My W refused to talk to the kids (14 and 17 at the time) about her plans to move (and take D's half the time!) until she had rented a house and was just days away from moving! She had been sleeping on the couch for almost a year and telling them it was because I "snored too loud", not because she (like every MLCer) couldn't stand being near me in bed. They all sleep as far on their side when still sleeping together. For my part, after telling her many times that we needed to talk to the girls and tell them what is happening, I decided I wasn't going to hide it or lie to them. When they asked questions I told them that their mother was going through a hard time and that she may be leaving. When the day came that she got the guts to finally talk to them (what she said was ridiculous when she actually did talk to them but that's a different subject) they weren't so shocked and handled much better.
IMO, and I don't know your sitch as well as you so you need to do what you think best, I would be honest with the kids. They have to see that dad is acting oddly. That the 2 of you aren't acting like H and W. When they ask questions just be honest. If your H decides he is definitely leaving but wants to wait to tell them, I would talk to them alone and give them a heads up.
They already know more than you or H think. They know that things aren't right. We always think they are much less aware than they really are. I think, when the time comes and you have that dreaded talk, they won't be as surprised as you think they will be.
