Here's what I consider a key point. Whatever issues your H may have (and imho anyone getting with someone that much younger does have issues, at a minimum stupidity), you can guarantee that out there in the world there are tons and tons of men who (a) are much more appealing than your husband in looks, character, life experience, kindness, decency, and personality and (b) would desperately like to meet you and treat you right.
Guaranteed. So, he should be very worried given what he's done to his own level of appeal. You should not. Speaking of the sex thing more generally... I figure this probably varies between cases even more than other stuff but I am reaching the conclusion that a down period was probably normal and necessary in my case. Immediately after d-day we had sex quite a bit, then it was upnand down, and then it kind of went to nil. The "nil" period coincided with big increase in my wife holding me or needing to be held during the night, but all kind of chaste. My libido was not down but desire for her was really low - like, I feel pretty horny but I can't be bothered with the effort. Not a usual feeling for me. I feel like that period might have been a necessary reset, so that there can be a clear emotional line between our sex life together and the affair sex. Because otherwise when I have sex with her it is kind of just part of the continuing story of her sex life including with him, and that's not okay with me, perhaps not okay with her either. Of course none of this is conscious, it is just how I am looking at it to try to make sense of it. The post-drought period sex did feel different, too. Which I also think is healthy.
Maybe it is okay, maybe it will be okay.
BS, d-day Feb 2017, 16 mth affair.