http://www.telegraph.co.uk/news/1928899/Men-'not-interested-in-sex'.html

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Increasing numbers of middle-aged men are going off sex, according to relationship experts.

Counselling and sex therapy charity Relate says it has seen a 40 per cent increase in men who simply cannot be bothered to make love to their wives and partners.
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I really, really wonder if their sexual "turn off" is more related to the pressures they feel in their relationship. Many women think sex is 100% physical when it comes to men (IOW, men can do it whenever, wherever, however, with whomever), but men actually have a psychological side that can inhibit their sexual drive every bit as much as, if not moreso than, women.