I agree with ovrrnbw. This is something that needs to be rectified. No matter what. His mere presence is going to continue to cause you angst and resentment. I know we've talked before about finding a new BS troop. If it is truly over between her and him then your W will support that.
I agree about this too. You have the reasonable right to demand that she suspend any interaction with OM. No more volunteering, find a different troop.