I think it is an assumption on your part that outing him to his W will send him into the arms of your W. It may do just the opposite and make him backpedal to try to save his M from blowing apart.
I don't think you have much to lose at this point, unless you consider the move dangerous in some way. Evidence might also be good, since the W could side with her H and choose to not believe you.
I can't imagine what it must be like tho, so this is just IMHO & FWIW.
SF
Spellfire aka Mike
"Women do not like controlling men. They respect and are attracted to men who control themselves. They ultimately are repelled by men who allow themselves to be controlled." -S&A