Oh the joys of vicarious living!
Can't really see what the problem is - you're both single. He's probably dead chuffed! Only thing I could say is to face the world with pride - nothing has changed, you had a great shag, and so what?
If you don't want things to go any further (and you've said you doubt he does) then tomorrow is just another day. It will probably do his ego good anyway if you behave as if nothing has happened.
Way to go girl!