My opinion is that she'll stay. Hey...it happens. Sometimes I think more often than not. I think men go through more of a middle age/elderly crisis than women do. Maybe they need some of them middle age pills and patches like us women have to use!
My thoughts may be the wrong attitude, but as long as a person does their job.....why be so worried about their "bedroom" life? Dang, that's personal. As long as a husband/wife, man/woman can work it out....or if they agree to what ever...so be it.
I agree that she must be very hurt, not thinking that he would do anything like that, but at the same time, she should also understand the man, with their years together and all that they have been through.