You're son's a teenager which by definition means that you've been setting a good example for him by words and deeds for at least 13 years. One night is not going to undo that. Of course, since he is a teenager and you have a close relationship he know the buttons to push and may not use adult discretion, but always remember you are the adult in the situation and you have the ability to frame the conversation.
I have 20 and 22 year old children who I'm extremely close with and I've found that if I made a poor decision it was best for me and them for me to 'fess up, talk about it, and if necessary apologize. As our kids get older they begin to realize that we're not infallible because we're not. We're humans who try to do the right thing and as it clearly comes across in your post be the best parents we can be. Unfortunately there's no script or playbook. Without getting too much wordier, I'm agreeing with the previous posters who have stated that you should address what happened.