Interesting responses....
FWIW, BF's wife has become very much a stay at home person, pretty introverted. Understanding BF's desire to be with people, she's always given him reign to stay out late (after work crowd getting home at 3AM) or be gone many hours on the weekend going places (including work), visiting friends, etc.
BF and his wife are basically friends with benefits. She's aware of some of his past affairs, certainly not all. Her attitude toward BF and my spouse is "you've told me, now don't mention it again". BF said sex life with BF's wife is unchanged (very infrequent, but good when it happens).
While BF's wife may have had an affair many years ago, BF says that she says, she has very little interest in sex, no real need for additional friends or companionship, and absolutely no interest in a lover.
SO & I theorize BF's wife is most interested in keeping her current financial/logistical situation -- she's been through it before, and while she prefers he not be sleeping with another, she has decided (again) not to let it upset things between them.