Starsky309 For two days I have been thinking nonstop about the question you posted above. Frustratingly so, I have not come up with any answers or a plan.
HINT: (and not to be morbid, but many posters report that this really works for them) -- What would your plan . . . your LIFE . . . look like if your wife suddenly passed away? What would your goals be? What parts of YOU would you want to work on, and how would you go about it?
25 is right -- your entire focus is on YOUR WIFE, instead of on YOU, where it needs to be. This also goes to your "How to act?" question, because if you are truly working on YOU, then your positive attitude will be an honest reflection of YOU and the changes you are making in your life. You want to convey a sense of "Hey, this is NOT something I wanted, and I'm CERTAINLY not willing to live in an open marriage nor do I condone your affair in any way. But to be honest, it's forced me to address some things in myself and in my own life, and honestly I feel pretty good about me these days. Not sure where all this will lead, or what's going to happen to our marriage, but I now realize that I'm going to be okay."
You can't FAKE that . . . you have to honestly get to that place. But you can START it, and doing your own "work on you" will help you get to where you're fully living that attitude in front of your wife every day. And as the women will tell you, THAT is damned attractive.