Firstly - in my opinion you mythologize too much. Women also like regular sex without commitments - typical ONS. Especially from the young generation... (1995+, more liberated). Secondly - you search too much for some deep motivations - and according to research, very often it is an impulse, a rush of the moment.
the author has put Vivian in a situation between hot desire and permanent love, a relationship in which classical desire has simply died out. The language of love that Vivian speaks of is precisely such a family hearth hedgehog.
Hutch understands the situation - that Viv needs emotions that he can no longer give her. He faces a dilemma - whether to end the relationship or try to survive it - in the name of love (because he knows that in the long run the fire of romance will burn out), 22 years of living together, connections. Such matters do not end in fifteen minutes.
but enough about that - we don't really know yet where
SC Stories wants to take us, and as I mentioned earlier - I prefer to focus on what is on "paper" and not on the supposed thoughts/situations/motivations, etc. etc.
ps. a woman's word would really come in handy in this thread.