I will resist the temptation to rescue W during the deposition, but I have decided that I will stop my L if he is insisting on getting W to tell intimate details about her relationship w/ OM. It doesn't matter to me if they are or are not having sex. That really is irrelevant. I think we'll just need to get her to admit there is a relationship and there has been an affair since November going on. That should provide enough backing w/out embarassing her to tell details.
I'm not sure I would set that strong a boundary on the questioning. If, for example, they are being inappropriately sexual in your D5's presence then the questions would be relevant. Since you have done the right thing and avoided using D5 to gather information, you don't really know much about how your wife and the dirtbag interact in her presence. Don't be too quick to call off the dog--he might smell something.
I don't have final exams for another week and a half...but my boys and farming have taken every spare minute I have for the past month--the trees have leafed out and we are through our first irrigation cycle.