In my best Inspector Clouseau voice..."The mystery is now solv-ed."
Let's examine the clues...(1) Mr.HP doesn't understand how important having sex is to HP. (2) HP parades nakedly before him regularly without getting any action. (3) Mr.HP will only sometimes spoon with his dog in her buns. (4) Mr.HP has a moving, fluid-filled cyst on his noggin.(that must be very attractive when it comes around to the front of his head )
There is but one conclusion. He has WATER-ON-THE-BRAIN!