Five years ago, Boy meets Girl. Boy likes Girl. Boy makes mix tape and asks Girl out. Girl says yes. Three weeks later, Girl breaks up with Boy. Boy and Girl stay friends. Boy wants to get back together with Girl, but Girl says no. Girl is friends with Girl 2. Girl 2 asks out Boy. Boy says yes. Girl says, "Rebound." Boy really likes Girl 2. Boy and Girl 2 fall in love. Girl, Boy, and Girl 2 all stay friends. Four years later, Boy buys ring and asks Girl 2 to marry him. Girl 2 says yes.
Today, Girl receives card -
"Thank you for being part of our special day and thank you for the Battle of the Sexes. We remember how it was really all your fault that we're together! Of course it's a fault in a good way :)
[Man and Wife]"
Girl smiles. A lot.
PS - Girl still has mix tape somewhere.