One evening, some time ago, my lover and I were hotly enjoying ourselves in bed. We were in a modified missionary position and situated haphazardly--nearly diagonally--across the mattress. When he ecstatically pushed himself into me, his whole upper body also moved forward with some force, which led him to repeatedly strike his head against the chiseled corner of my wooden desk.
After I noticed him hit his head for the second time and realized that he was too entranced with our fucking to protect his frontal lobe, I unhesitatingly extended my upper body and placed my forearm between his forehead and the hard-edge of my desk. It took him a moment to notice the change, but when he did, he stopped inside of me, met my gaze, and smiled slowly at my kindness. Then he sweetly kissed my forearm. Exactly in the place where his head had been protected.
On a very elemental level, I feel that this is what relationships should be about. Unhesitating protection.