The boys are on tour right now. They just arrived in Vegas and check in in their hotel. Normally they had a room for them self but management messed up their room arrangement so Louis and Harry agreed to share a room. Nothing special just two best friends sharing a bed. What could go wrong?
Or: the one where a dream turns into reality and friends with benefits is not an option.
Louis and Harry were friends since they were little. Best friends actually. When they were 17 they finally moved in together. It wasn't complicated at all till feelings get in their way and Louis disappears. Leaving a worried Harry behind.
Or: The one were a dance ruins Harry's and Louis' friendship, and everything changes.