I do not think you are making this up, as some people have outright claimed. However, I do not think there is anything paranormal or supernatural about this experience. Do you have a back door? Or any other door that leads into the house? If not, what about windows? Are they all locked? It would not surprise me that a drunk guy found a way inside your house.
You said he did not live across the street anymore correct? He probably did not have another place to crash that night, or being drunk, chose your
place. Perhaps he had been there much longer than you thought, or he thought, since he had been quite intoxicated. Not remembering details means he
was likely extremely drunk, so that part is not surprising in my opinion. I personally usually remember some details even when really wasted, although
I stopped drinking a few years ago altogether, since I tend to get stupid and make a fool of myself, lol.
He may be different, but I assume it takes a lot of alcohol to make you forget such critical details. That really is not even a detail, but an
integral part of the story in my opinion. So he was too drunk to remember, arrived at your house, found a way in and went to sleep. Seems the most
plausible explanation. As to how he got in, I think you may be overlooking something, or underestimating the tenacity of a drunk on a mission, lol.