All I know is from talking to divorced female friends I learned that their DHs weren't that keen on sex, and repeatedly rebuffed the wives. The affair partners were totally different to the wives.
(Can't say too much as don't want to identify people)
eg. Professional women wife, high earner, degree educated - husband also degree educated, lecturer - OW = biker chick, unemployed, lived in a squat. (Wife ended up with an STD)
Businesswoman wife, high earner, - husband manager for charity - OW = no qualifications, 10 years younger, worked sorting old clothes at charity shop.
Wife healthcare professional, degree educated - husband businessman - OW = no quals worked in a fish shop.
Husband s/e tradesman high earner - wife business owner - OW = hospital cleaner.
I would say Madonna/whore complex but then I'm not a psychologist