For starters I'm struggling with the we never had sex part. Come on you're going to give up your current life with some guy at work and you're not going to see if the sex is any good. Pardon my French but she's full of shit. Now that the obvious is out of the way you need to think back to this time when she was having this affair and try and remember what you can. We're you guys having issues? Dead bedroom? Arguing? Was she disappearing? Keeping her phone close? Behavioural stuff. This whole thing is a tough pill to swallow. It's obviously you're call. Me personally I don't think I could get past the betrayal. If she doesn't get sick she's gone. She gets sick and now has a revelation but this still makes you number 2. The consolation prize. Not a place you want to be in a marriage. Whatever you decide I wish you the best in this shitty situation.