My first concern would be that you would start to become irritated constantly trying to ride at his speed. Is there an opportunity for you to ride alone at another time maybe?......or how would he feel if you start out together, finish together but you take off on your own in the middle. Maybe leave him after the first mile and he turns around when you reach him on your back? I don't know your dynamics but if you leave him alone and wait for him to suggest it - would he? or is he counting on you to motivate him off the couch?
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"