TS, does it matter if your wife went out on a date or had an intercourse with this guy? you are only hurting yourself more. being emotionally involved with this guy and lying to you are enough to break your trust. i understand wanting to know the truth, but you want to work things out right? it has to start with your wife, since she did you wrong. it maybe good to take a breather, apart from each other...because being together only makes you want to uncover more of the truth and doubt her.
this might teach her a lesson that if she does this again, you could be gone in her life. honestly if it were me, once would be enough since i've already suffered enough of this when i was still in the dating scene. tell her you know the truth, even if you don't know all of it. the guilt should eat her up if she has one. draw the line and make sure she knows her place.