Milk production works on supply and demand. The more demand there is, the more the supply will increase and vice versa! So if he's only eating on one side and you pump the other, you'll just keep producing that much more on the other side. It sounds like he's just settling down on his feeds and getting what he needs from one side. If you don't pump, your breasts will accomodate over time. If you're worried about mastitis, you could just decrease the amount you pump out gradually, a few minutes a day, until you stop pumping at all, so that your breasts get used to it slowly. Just make sure you switch sides for each feed so that each breast is emptied and stimulated. Do you offer the second side at all? If he goes through a growth spurt, you might find he's interested in it again!