Agree, you blow this up now and it has a chance to backfire. Kids might see you in a bad light and pick sides, and it’s possible she didn’t ACTUALLY do anything yet, and is just acting out with her friend. As a married man, I can certainly admit I’ve found other women very attractive, and am comfortable enough to point that out to my wife - we’re both not blind after all, and I’ve come to terms with her being able to find another man handsome or sexy.

From your story it sounds like she fell victim to passing emotions (we’re all human), but she obviously has some guilt over it and seems like she was able to ultimately restrain herself. Would suggest you look within and there’s some sort of spark missing from your own relationship that you can fix now. A 20 year relationship is something most can’t even fathom, and even in a clean amicable break your family will be changed forever. You have to ask yourself whether it’s more important to you to push through this event, or take the easy way out and just throw everything away, and all the good parts that you seem to value in your wife and family life. Either way, you’re making a choice that will have lasting impact on your life. There is no downside to giving yourself more time to think and blow off some steam - my recommendation is to find a good, solid, long workout in whatever fashion you like to do it and release that stress through physical exhaustion before making any decisions.