Ouch Michael,

A little advice from a happily married woman of 20 years who is married to her best friend - Praise God!  
It does not ever need to be that way you describe.

God made us both passionate in love and passionate in body.  You can seriously damage your marriage treating it like a responsibility more than a powerful experience of releasing desire and love.  Sex, in my opinion, and your wife might surprise you if you change things slowly and gently over time, is about allowing the animal part of you to be set free.  Men and Women are designed to be turned on by touch, feel, smell, voice, taste - follow your instincts- your primal drives instead of caging them, and explore your wife this way more, and you may find she awakens her own drive and starts exploring you more.  This shared animal pleasure results in an honest sexual relationship which ends up supporting a spiritual and emotional closeness too.  We can laugh at each others funny fantasies together but still enjoy them