Re: Wife is behaving weird. Need some input
Given the problems you describe having in the past, it is possible that, at her age - and because of hooking up with an old friend - she's reached a point where she just wants to live out the rest of her years the way SHE wants to. She's obviously getting her emotional needs met by this friend (assuming it's not really a man she's having an affair with), and no longer by you. Once that happens, women often simply stop loving you, except in a platonic sense.
And many women DO believe that sex is just an obligation. I'm one of them. My H always makes it great for me, but I don't want it; I just want to get it over with, and then I can relax for a few days, knowing he won't make moves on me for at least 4 or 5 more days. And I can't wait until he's no longer interested in it. As sad as that sounds, a lot of women feel that way.
That said, if my H would fix all the problems I have with him, he would become MUCH more attractive to me, and I'd be far more interested in having sex with him. All the things he does that upset me keep me too turned off. So I'll urge you to take a REALLY hard look at yourself and see what it is about you that she's fed up with, given up on changing, or barely tolerates. We can help with that.
Finally, what you describe sounds A LOT like she's having an affair. Don't stop snooping and following until you know the truth.