I really don't think he'll be civil. For a start, he'll be really pissed off you've found out. You will be taking away his stable base, and causing him hassle. He'll have to find somewhere to live (he can't move in with OW) which will be hassle, and cost him money. If you currently cook his meals, and do his washing, he'll have to do that himself, so that's more hassle.
This isn't a decision you've mutually decided on, you're pulling the rug out from under his feet, so he'll do everything he can to punish you.
You can hope for the best, but you need to prepare for the worst. Park the car somewhere else, and hide the keys. Also, plan for how to get DD to school, in case you find all the tyres mysteriously flat one morning.
Did the solicitor tell you how much it would cost to force the sale of the house? I'd heard it was expensive. Even if you get a buyer soon, he can drag his feet over the sale. The average sale takes about 12 weeks, from offer to completion, but could take months more. You're going to have to find somewhere to live once it's sold, but I'd get that ball rolling now, because once you've told him, if he refuses to move out before it's sold, you can't carry on living under the same roof, it will be hell.