I'd bet money that this guy was all nice and willing to pay for things while the cop was there, while witnesses were there, with no intention of following through.

Go after him. Press charges. And get that knee checked out.

Don't feel foolish. He's counting on that.

You were struck by a car while on a bike. YOU'RE not the one who is supposed to feel foolish, guilty, or even on top of your game. You were shaken up and took the guy at his word. His word wasn't good.

Now you go press charges. I can't imagine that it's too late.