Not sure what others will say, but I would have to confront her about that.. not because she's sleeping with him, but the fact that they kept your D up.
For God's sake go downstairs to the spare bedroom. In my sitch, I would definitely confront her and him. No excuse for that.
Maybe you should ask W about what your D said. It's not like you were asking for the info. I would approach it as "Hey.. D said XYZ.. are these things true.. if so, do we need to make different arrangements with D? I'm not comfortable.. yadda yadda yadda."
Man.. that sucks. There is no easy way to deal with the physical. You just have to get bye it. One thing that kind of helped me was thinking.. "Well.. she wasn't a virgin when we met, this is really not that different"
Of course it is different, but that's what helped me mentally.
Spend time with your D.. focus on her and forget about this other trash for now. I know it's not easy, but you can do it.
