If you keep drinking it will more than likely happen again. If you don't tell him and he doesn't find out, put in that same situation again (drunk w/ charming stranger) you will probably be drunk enough to think, "hey, he didn't find out last time, what the hell."
It's up to you to decide if you are going to tell him or not, you will forever feel guilt about it. Whatever you decide, make sure you do it for the right reasons.