I wan date my bestfrend but he went with my twin sister what should I do ?

Laugh about it in public, cry about it in private, and someday say lightly and with a smile 'Gee, I wish it had been me' just in case there's that one in a million chance her really did want you but thought for some reason you didn't want him. If he laughs it off or seems nervous, let it go, forever. We all of us are attracted to people we can't have sooner or later. If you can't be friends because you are in love, tell him so and tell him why.