Pole atiriri about your hurting friend. There are very many theories about why we "cheat" on our women. The rule is "innocent until caught pants down". What i can tell you is that it is a stark reality that we will once in a while stray. I think the best thing for your friend is not to try and revenge for the sake of revenge but to continue loving her man especially if he is not abusing her. Loss of sexual interest in a wife by a man is not a loss of interest/love in the wife. If she feels sexually starved, it is not real sexual starvation as in the case of a man but rather a need for intimacy with her man which she will find she can resolve in other ways without sex. Let her talk to almost any older woman and once they open up she will find the older woman has the same experience, and almost all women in the world.
Assist her find frank ways to open up and express her fears without fighting, but if he is an abusive man, she is better of without him.
Ras Kienyeji Man