If you think about this, a "couple who messes together stays together." Messing and changing each others diapers is perhaps more intimate and trusting than is intercourse. You are lying down on your back in a vulnerable submissive position placing all your trust in your partner to gently and lovingly clean you, perhaps then followed by passionate love making before a nice fresh diaper is put back on. Sexual intercourse is expected in a loving/intimate relationship; while changing a messy diaper is, well, we have to admit it, on the fringes, and therefore requires a lot of trust to share this part of our lives with someone. Acceptance is one of the greatest gifts we can give each other; while rejection is the most painful human emotion.