Sorry to be stuck on this but ... My MLC/WW had a full blow delusional EA with an OM, but backed off after I immediately punctured that delusion. I just did not think it was good for her mental health to hang on to an absolutely delusional view of reality.
Anyway, my suggestion isn't really to have a confrontation, fists cocked, ready to punch the SOB. In fact, I believe the poor young man is a completely unwilling pawn in your W's delusion, feeling totally weirded out that his boss is coming onto him, and will be relieved to know that you are sympathetic to his plight.
What is there to gain? One, I get the sense that you buy into your W's delusional fantasy; and I think just talking to the fellow will help you get a better footing on reality. Two, after you talk to him, you may be able to find a way to gently but firmly shine some light on your W's delusion. Get her back to reality.
I'm not trying to bludgeon you with my logic. But I respectfully submit for your consideration. You know best what's going on in your situation.
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final