His parents are quite well off and quite old how where does he stand in terms of wills and inheritance?
In that case, he should go for a quick divorce. That potential inheritance will not be take into account, as it would depend upon the will being in his favour.
A female friend’s husband screwed around for many years and was unwilling to collaborate in the run-up to a divorce, delaying it for years. (He claimed it was against his religion). Once he learned that he was to be the beneficiary of a sizable will, he divorced damn quick.