I agree that a healthy, open sex life might keep both partners interested in each other (I hate the term dirty...as if there's something wrong w/being more open "between the sheets"). However, sometimes it doesn't matter what one of the partners is doing; some partners crave that excitement...that feeling of lust and response to the increased level of pheromes...that comes from either the "chase" of new or different people and/or the actual experience of being w/someone new.

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Communication is the key.