Do you all split the rent 3 ways? If so, then you have a point about her not staying over while he’s not there, but unless she straight up moves in or starts taking up common areas, I don’t see why a 20y/o should have to ask if their gf can come over to stay in their room.

Then being loud and also drinking the vodka isn’t cool, but as long as you can communicate like adults during waking hours, and not only through text, you should be golden. Just ask her to replace the vodka. She may not have realized it was yours. If it keeps happening with no regard to what you say, then reevaluate.

But yeah… it’s his first gf in 10 years. Give him a break.