According to a recent article at PsychCentral, the most difficult couples to work with in couples' therapy is "Mr. & Mrs. Just Not Feelin' It". This is the the couple that are technically still married, yet they are functionally divorced. Oftentimes you'll find couples like these being non-sexual towards one other and even sleeping in separate quarters. Though these couples are living in a cold, distant, and loveless relationship, many times they can "fake it" and endure to a degree that their children, friends, and extended family have no idea of their despair.
Though such a couple can present several challenges to the therapist, a skiled and caring couples' counselor will be able to deconstruct their arguments, posturing, and reticence to help guide them towards a mutual appreciation and a robust relationship.
Read more about "Mr. & Mrs. Just Not Feelin' It" by clicking here: http://psychcentral.com/blog/archives/2014/09/03/couples-you-meet-in-counseling-3-mr-and-mrs-just-not-feeling-it/