I rear ended someone today...?

Okay first of all, he can't bring this back to light BECAUSE he left the scene of the accident as well. Yes it was your fault, but the insurance company will want a police report. Did he stay for one? Nope. So technically you could even keep from paying for his repairs, but that would be dirty. Just check at the shop when he goes at the same time and come to an agreement on the repairs. Don't tell your insurance company or his. I had the same thing happen to me but I was the one rear-ended. I had a police report done, but I never did anything with it. It just went away. So don't worry so much, just talk to him. He can't screw you over now.