You are getting some great advice I just thought I'd add a couple random thoughts.
I love the fact that you are making the conscious decision to look great and act confidently whenever you leave the house. Go get 'em cougar; be the hottest, brightest TW you can be.
Their affair WILL implode. It simply will. Affairs area fantasy world and the fantasy evaporates when faced with the real world. Then challenge will be deciding what you want to have happen once it does. (that may not be as straight forward as you think)
Do the 5k! Just do it!. Join a running or exercise group that meets regularly, cross fit, yoga, whatever. The regularity of the group will provide you with some cameraderie (sp) the endorphins act as an anti depressant, and the physicality will give you confidence. Also have your kids run the 5k with you. Our 10 year ran one last fall and he was by no means the youngest.
One final thought. As I was reading your posts, I had this image of a really active, focused Mom, there for her kids, rockin' it at PTO, play group, bunko, etc.
Is there a possibility that you devoted yourself so much to being a Mommy that you forgot to be a wife? I ask because that's in part what happened in my world. My wife became Mom to everyone, including me, assuming that if I was taken care I was happy. I really didn't need to be taken care of.
