I rewatched the sex scene and you're right, it is difficult to explain. :/ Which is a shame, because in the scene before where they look at the locker, Naomi obviously *is* really freaked out about it. So the progression from that to giggly sex doesn't make a whole lot of sense.

I think I'm going to watch the episode again and then do a big meta post about why I thought the lying and cheating was in character for Naomi.