Difficult question to answer in simple terms.
A lot of married men, or men in long term relationships, still punt. Having chatted with a few prossies over the years, the general impression I get is that this is for two main reasons.
Firstly, the wife or partner has gone off sex or started to ration it, often after having kids, sometimes because they don't think sex is normal after a certain age, or because of the menopause which has killed their libido.
Secondly, sometimes the wife or girlfriend will not scratch a particular itch, such as a desire for oral or anal sex, or try any new positions ( I've had at least two partners who wouldn't try doggy style because "It wasn't romantic" ) or maybe the male wants a bit of tie and tease or rough sex, and that's voted down straight off.
Is sex better with a wife or g/f? In my opinion, the emotional side is better, you know that you are screwing someone who wants to do it with you, and not because you are paying her, and that's a bit of a buzz, but the physical pleasure is no greater. Sometimes an SP can actually provide greater physical pleasure, but of course there's no emotional connection.
Also, sex with the same person every time can get boring if they aren't willing to experiment a bit, it gets predictable and like baked beans every meal.
Hope this helps.
