There are problems connected with infidelity and problems connected with being faithful at any cost, and I am for letting those concerned choose the problems they'd prefer. There need not be one rule for all. Infidelity is enlarging and fragmenting and very very dangerous, but it has been known to retrieve people as well as marriages, so it can't be only bad.
"Some Men are More Perfect Than Others". Book by Merle Shain, 1973.