Thanks for the comments, they're very helpful. As much as I want to get into the mindset that the A is not my fault (I know that it's not), there ARE things that I did or didn't do that probably made her more vulnerable to get sucked into someone else's wiles. And I do want to take this time to work on myself in general, not to get her back but to make myself a better person no matter what happens in the end.
I should have explained more in depth about the exercise: I realized that exercise would probably help me in the sex department, so I started doing it regularly for a month or so. Then my wife started the A and the big downhill slide occurred, so my exercise backslid a bit. I didn't feel motivated at the time to do it as much anymore. Now I'm getting back on the horse.
It's not like I'm bad in the sack. Our sex life was pretty good when it happened. I think that the big areas that needed work were variety, more self-confidence and less hesitating to try different stuff on my end, and perhaps being more knowledgeable about things that I could have done. I had a certain bag of "tricks" that worked well for a while, but I'm sure that she got bored that I did those same things every time. In fact, I feel like her sex life with OM is primarily fueled by the fact that it's all so different! (The "positive mirroring" that she gets from him contributes, too -- she probably feels more attractive and wanted because of his constant affirmations.)
I like the suggestion you gave Julz about seeing a doctor. I've also wondered if maybe my testerone levels are lower than they should be. I just plain old don't feel all that sexual most of the time, and I feel that maybe it might be physiological rather than psychological...
