That can be very frustrating when, no matter what you do, the ball keeps coming back. It's even worse if the other player can keep you on the run. You will need to find a way to make him alter his game plan. A few options-
-Are you familiar with Wardlaw Directionals? If not, you may be doing a lot of running because of poor shot selection (hitting down the line and then having to chase a cross court reply).
-Have enough firepower to keep him off balance. Probably not realistic for you.
-Get to the net. Sounds like you already thought of this.
-See how he handles off pace shots. Slice, drop shot, hit some loopy groundstrokes. I have seen many HS players that mimic a ball machine - basically the same shot over and over. Once a slightly better player gets used to this you are in trouble.
You might not be able to beat someone like this right now. It is good that you realize that you should have tried mixing it up by coming to the net.