Okay, to be perfectly frank (and I apologize if this offends you or anyone else reading this), you can go to a hospital ER and request a rape kit. This will show whether or not there is anal tearing, even though the unknown event is now several days past. I do appreciate that you may not truly want to know what happened, and that's certainly your prerogative.
Yet, if you're resigned to the idea that you "will never know what actually happened," but continue to obsess over it with no intention of doing whatever you can to discover the truth, you're going to make yourself crazy and invite a steady and powerful stream of emotional and psychological reasons to continue drinking.
As I've said before, your best option may be to seek counseling for this since this event and the fallout afterwards have left you hurt and confused, a difficult place to be when trying to sort things out and take the proper course of action.