I was hoping the desire would go away with the erections. Of one thing I am sure. You and the wife will deal with this together. And the way you have dealt with this shows your commitment to her. ie telling her to take a lover which she refused. I am 67 and feel the small changes I don't like. And the not feeling like a man. Believe me sir you are a man that should be admired by all. Offering to give your wife to another for sex is the most unselfish thing I have ever heard or. And your loyal wife has the same quality. As girl crush stated "hang in there" things got a way of getting better."
A friend who has your respect. Charlie.