I don't see what you think you done wrong but if you believe so then so be it.
However although you think this I'm sure your boyfriend will understand the situation considering the fact that you got very drunk.
If you really feel guilty about it then just explain to him what happened and assure him that there was no meaning in the matter, like I said I'm sure he'll understand.
I guess what you can do is make sure the guy you went home with doesn't read into the head on shoulder, arm around you, holding hands thing; but then again he might not even read into it... since, I assume, you were clearly drunk.
What you can also do is thank him for taking you home safely.