Shmiras Einayim

The gemara says that Tu Bav was a VERY happy day. The boys used to go out and were told "שא עיניך" "Raise your eyes" and look at the dancing girls and choose a mate.

Chasidim say that it is such a happy day because the boys didn't want to look and had to be TOLD to look.

[Heard from the Rebbe Shlita]

Also  - the gemara says that the only people who went to the vineyard were the single boys, meaning that if a person already had a wife he wouldn't go "just for fun".

Also the girls lent dresses to each other. Chesed.

[Rav Dessler]