Rabbits will normally only live together if they grow up together from being babies. You could try to get him a friend but it depends how long he has been alone. If he has been alone quite a while he probably wont adapt to a new friend. I tried this once with 2 of my own bunnies but they just attacked each other so now they live happily on their own. As long as your bunny gets lots of attention from you i don't think you have anything to worry about as he will be very happy.