I can identify with much of what Freddy says above about the behaviour of (potential) marriage partners, before and after the event. Certainly, it is natural to be on 'best behaviour' during the dating phase and the period immediately following marriage or co-habitation - and this includes indulging the partner in ways that might not always be acceptable and are, in many cases, unlikely to last. Obvious examples (aside from choosing clothing or personal appearance to maximise visual appeal) are being generous with personal gifts, eating-out, entertainment of all types, transport, practical tasks (such as DIY or needlework, tax returns), helping or caring for needy relatives (children, old people, potential in-laws). We can all think of things we cheerfully gave or gratefully received and which may not now be forthcoming, at least with the same degree of generosity.
I don't think that sex and other aspects of an intimate physical relationship necessarily go hand-in-hand with the above. Such favours may be given or received regardless of the other 'gifts' and are more likely to be affected in the longer term by age or infirmity, i.e. the spirit may still be willing but the flesh becomes weaker. Conversely, as outside demands (job, children, mortgage) lessen or indeed disappear, the ability (availability of time, money) to provide more material tokens will normally improve - at least until the unfortunate time when poverty in retirement may limit one's resources, especially if health-care has to take priority.
In my case, neither my first nor my current wife has proved to be the person I wanted to marry, thought I was actually marrying or did indeed marry; both changed in behaviour, outlook and attitude towards me in a way which has significantly eroded my self-esteem as well as my respect for them and my day-to-day enjoyment of life. But, that said, both marriages were 'right at the time', as they were evenly matched and showed great promise. I cannot honestly say that, if it history were to repeat itself, I would not take the same action again. The saving grace has been that my first marriage produced two fine sons and my second 'included' three fine stepsons. In both cases, my wife's willingness (and apparent pleasure) in, amongst other things, 'dressing to please' soon evaporated - and not directly as a result of childbirth or age - and any hints or requests for a resumption were treated with derision and, often, suggestions that I was a pervert. (And I'm not talking here of anything extreme such as bondage or fetish wear - merely stilettos, stockings and other essentially feminine and elegant or glamorous wear on the right occasion. Has the concept of 'dressing up' for an occasion really gone out of date; I generally do - she rarely does?)
My wives would certainly agree with Freddy's closing remark that men are at least as much at fault as women. Whatever I do in terms of personal conduct, bodily hygiene and clothing/appearance, I am subject to criticism and in some cases ridicule. Fortunately, my health is good and I am neither hideous nor overweight nor lacking hair in the right place - but some loss of teeth and hearing is treated with little sympathy.