"In a lot of middle-aged marriages, sex has become victim to whatever the relationship's issues are."
If you aren't addressing your relationship issues with your wife, aren't doing your fair share of the chores, etc., then it is not remotely surprising that she's no longer sexually interested in you (not necessarily you personally - but one) because those sorts of relationship disconnects may not impact your desire but they absolutely are going to impact hers. Many (but not all) men have a huge amount of patriarchal entitlement to their wives, believing they owe them sex no matter what as long as they love them and are faithful - and that's yet another libido killer for her.
There’s a powerful tendency in long-term relationships to favor the predictable over the unpredictable. Yet eroticism thrives on the unpredictable. Desire butts heads with habit and repetition. It is unruly, and it defies our attempts at control. So where does that leave us? We don’t want to throw away the security, because our relationship depends on it. A sense of physical and emotional safety is basic to healthy pleasure and connection. Yet without an element of uncertainty there is no longing, no anticipation, no frisson.
Perel, Esther. Mating in Captivity (p. 33). HarperCollins. Kindle Edition.
Obviously, that applies to both partners but disregarding the long history of patriarchal entitlement to wives time, attention, and bodies is a miss. It's not overt the way it used to be, but there's plenty of that lurking just under the surface in a lot of relationships. Of course, sometimes wives take their husbands for granted, but 70% of divorces are initiated by women and they say that is one of the major factors - that they are taken for granted, that their husbands won't put any effort in on trying to maintain the relationship, etc. Guys who do that stuff and who treat their wives like lovers all along have fewer problems in this department.
