My FI was invited to a gala at his med school next month and the invitation says black tie optional. I am clueless here. I know the rules and everything for black tie optional events but I am not really sure what I should do in this scenario. Should I opt for a short dress since I don't go to the school and would just be a guest? That is what I am leaning towards but since it is a longer event with dinner I feel like a long dress may be more appropriate. I don't know anyone else who is going to this so I can't ask any "what are you wearing" questions. It is at a very nice hotel with cocktails and dinner. That is really all I know and I am not sure what the appropriate course of action is here. Help is much appreciated.