Should a wife stay married to her husband if she has allowed herself to fall in love with another man who is twenty years older than her?

Yes! The age of the other person has nothing to do with it, but commitment to the person you are already married to has EVERYTHING to do with it. The grass often seems greener on the other side of the fence, a saying that has arisen for good reason. Although it would appear to you that this guy is far better and lacks the failings of the husband, he almost certainly will seem just as boring with as many bad habits when the present feelings fade a little - as they will! Unless there is serious reason to leave the marriage such as infidelity on the husband's part or abuse - real abuse and not just normal differences of opinion - you'll just be making a whole lot of people unhappy, either now or down the track a little.