Peeing is often a release of stress to a dog and they pee for a variety of reasons. If you google the terms peeing or urination in dogs, you can read all of the reasons a dog can find to pee besides that of a full bladder - and they are many from fear, stress, anxiety, marking for status, instinctual territory marking, to a sign of ultimate respect but he undoubtedly is feeling lonely, anxious and stressed when you leave, doesn't understand why you leave him and pees where it serves his needs best. You're just lucky he can't get to your bed and do is smack dab in the middle of the duvet where your comforting scent is concentrated and strong!
I'd leave him just two or three large towels to lie on for a while and toss that bed until he's given up the habit, once he's trained to be less stressed by your leaving. What is his age and activity level? Does he have pee pads to use when you are away or is he housebroken to potty outside?
If he's got separation anxiety, you can desensitize him to your leaving so it's not stressful to him and he'll learn to accept it and once you're gone, he'll know you're coming back and just eventually give up, lie down and sleep until you return, waking occasionally to drink or eat, patrol his area, relieve himself if he's got pads inside and then back to sleep.
Have you tried training him to accept your leaving the house? What kind of daily exercise or obedience training does he get on a regular basis? Be honest! LOL. No fudging on this answer!
