Is there such a thing as too much affection? Am I being a jerk?

Just tell him how you feel, let him know that you are a busy woman! I'm sure he'll understand. Just see if maybe he could change for you, learn to back off a little bit, but make sure that you also put enough time aside for him. Have an honest, open, mature conversation with him about it. Maybe he's trying to tell you something with his clingy actions?