Party to know that today is the last day we will be together. After this date all have to go to separate places. And no opportunity to be together again.
Parties to know that today is the last day that we are together. Because after today. everyone wants to learn each other and probably did not have a chance to get together again.
Theme to know that this day will be the last day we will be together after this date because they have to go to a different School and would not have a chance to be together again.