For those who don’t know here are a few things that happened on this day:
In the final year in the desert the Jews understood that they won’t die that year when they saw the full moon on the evening of the 15th of Av.
People of israel were allowed to marry people from tribes different than their own on the 15th of Av.
People of Israel stopped boycotting the tribe of Binyamin and also started marrying them on the 15th of Av.
On this day, every woman that was single in Jerusalem would lend her friend a white dress and borrow one from one of her friends. They would all go to a central place in Jerusalem and would talk to single men. The men couldn’t know who was poor or rich, so they would be honest with their feelings.
Because of a few reasons mentioned above, this day is known as the Jewish Valentine’s Day
If I missed some stuff, feel free to tell me!