How long really should a spouse wait just before becoming concerned that sex is not a priority in the relationship?

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Question by Has3BeautifulAngels: How long ought to a spouse wait prior to getting concerned that sex is not a priority in the relationship?
How long ought to a spouse wait just before being concerned if sex is refused or put-off in a relationship? This is based on no other individual in the picture (cheating) but strictly a marriage where one spouse does not want or ever really feel like having sex but acts like it is perfectly normal. Or possibly this is

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