His big sister started dating one of his friends. That kind of friend with who we party all the time and with who we like to share drinks, hangovers and everything in between, even girls. This time is his sister was the girl to share, it took a bit more to accept the idea. The friend liked the idea, he was afraid of what his sister would think but the truth was that she was even more excited than his friend, and after a few drinks it came all natural.