I am 9 months on from the day I found out
.
I don't have any answers, though on many days it feels better than it did at first, but it is a terrible roller coaster.
This is a link which might give your husband a few ideas about what to do to not make things worse. My husband did most of the things on the link, and they felt awful to me. The man's manner and voice might be a bit annoying to you, but I thought this would have been helpful to us 9 months ago. I think it might be worth listening to the whole thing, even if at first you don't think it is going to be any use.
I struggle with recurring terrible thoughts, and one thing which has been helpful to me is to say to the thoughts: "not now". If I am in a reasonable state of mind, this can work.
I also am trying to take care of myself, and this includes superficial things things like buying new clothes (which I never normally do) and trying to eat healthy food, but also deeper things like trying to become a happier, more positive person, trying to address my personal flaws, trying not to hide my head in the sand. This is incredibly hard, and I can't say I am doing all that well, but I know it is crucial for me.
Yoga with Adriene helps me. Talking to my one very close friend who knows everything helps me.
Realising that you can have a second marriage to the same person but you can't return to the first marriage is probably helpful, but I am not strong enough to be there yet, unfortunately.
Reading stuff online about how impossible it is to get over an affair (that includes most of what is written about affairs on Mumsnet) is one of the things I do which is not particularly helpful. Stalking the OW on Instagram, which I also do obsessively, is not very helpful.
Every day I have moments where I am overwhelmed, flooded, by feelings of terrible pain, and I question everything. Slowly, these moments are getting further apart. On most days, I do believe that sticking with your long term partner, realising that getting through this together is a chance for both people to grow and become better humans, can be a precious and idealistic thing to do.