I am a man, married for 20 years. My and my wife get on well, except we no longer have sex. We have had limited sex for much of our marriage, not very often, and very routine and unsatisfying for both, but the last two years have been barren. we live as brother and sister. I feel frustrated, and desperately want regular sex. We have both lost our confidence in ability to turn each other on. I feel sad about this and am considering leaving her. Is this unreasonable?