For my sitch, my kids know vaguely about mommy and daddy are “separated” (not living together) and things are different. When they asked me whether we will divorce, I was honest and said I don’t know.
Now things for me seem to be heading towards D, but I don’t plan on telling my kids until our d is finalized. And when that day comes, I plan on telling them the limited truth. Limited truth - not telling them that their father is a depressed alcoholic who is going through a MLC, but something like sometimes people go on different paths of life. I will always care about their father, but the kind of love will be different. Also like LH said, when they are older and asking questions, I will not withhold anything from them.