My husband would be dead after such confession...

I think that they should first of all tell the husband that anal sex can be had between them, not just between two men. Second of all, the wife should tell the husband also that confessing such things after the fact does nothing and is considered cheating, regardless of whether or not it's "just sex."

Honestly, at seventy-one years old, to have the audacity to say to a partner of twenty-six years, "Oh, I just had sex with someone else, but don't worry, it's just sex," is quite irritating and I would not want to be with such a person.

If the husband's ultimate "sexual desire" is to have anal sex with other men, then that's what he should do. And it's wrong of him to encourage polyamory on someone who seems to be monogamous. It also seems as if the husband is saying, "I want to see other people, but let's stay married." Which, if that's the case, is achievable, but not necessarily ideal. It's not polyamory, it's just having marriage as a legal document. Not for everyone, true, but it works for some.

I hope that this helped, I feel that my response was a bit of a disjointed jumble of cynicism and personal distaste for infidelity.

The fact that he went out and did this without having a long, deep conversation with her first is the problem. That it is sex with another man is immaterial. Assuming they didn't have an open relationship beforehand, he cheated on her- plain and simple.

What should she do? That depends completely on whether she wants to have an open relationship. If she's accepting of that, then so be it. If not, she needs to reevaluate whether she can stay married to a man who doesn't value their marriage enough to talk about his feelings before he acts on them.