The fact that you're hesitating shows this friendship means something to you.
Have you ever asked for payment? Could be a barter in return for him paying for balls and court fees or even repairing your leaky roof.
If you have not broached the topic, give him a chance. You'll feel better dropping him too if he still refuses to pay.
Check out the restringing charges around your area. See if you can charge slightly cheaper for a friendship discount as long as you can cover your costs. Your time ain't free too!
I made the mistake of not enforcing payment for a doubles group. Together, they owe me more than a grand now!