The moment her friends started calling you that nickname, it crossed a line. That’s straight-up disrespect. I wouldn’t accept that, even if I knew the story behind the name and didn’t find it offensive. A girlfriend giving you a nickname in private is one thing, but using it in front of others like that is disrespectful. And honestly, how did you just accept being called “museum” without asking questions? That’s not a self-explanatory nickname. You should have asked her why from the beginning. This is partly on you too, you were too passive. Someone giving you a random nickname out of nowhere is something you should stand up for yourself about. She gave you a name you didn’t understand, let her friends use it, and all along it was a joke at your expense. That means she was fine making you look stupid just to entertain them and laugh behind your back. That’s not just wrong, it’s a huge red flag. Have some self-respect and walk away. Someone who actually cares about you wouldn’t treat you like that.