Okay so last week when naomi's sister shows up she is talking to Ethan and she says "Don't worry i won't tell Naomi i was your first" So obviously they were together but did they Zeigen that in the early episodes???

as far as i know they didn't.they didn't even indicate that ethan Lost his virginity to someone else than naomie. i always thought it was her, so that came all of a sudden.
but to answer ur question: they didn't Zeigen that before