ESH. You’re not an asshole, but the way you handled this wasn’t wise either. She asked if she should be worried about anyone there (NOT if you’ve slept someone there-past partners aren’t automatically a threat to the relationship), and you gave her an answer that sounded like a long, detailed “yes”. Right after she got that answer, she went to a party where she met her boyfriend’s much older friends for the first time, which is a nervous situation in and of itself. Now, the party also includes the subject of that “yes”. And since you guys are long distance, it’s likely that this was a once in a while time you had to see each other, which she probably was looking forward to for a while and imagined that it would be magical. Instead, it sucked majorly, which had to have felt almost heartbreaking.

Your girlfriend didn’t do the right thing; her behavior was inappropriate. But she didn’t exactly do the unexpected thing either. It’s likely she drank the alcohol in the hopes that she’d calm down, but the opposite happened.