Perhaps misunderstood? (Spoilers)

I understand the "WTF" reaction as I myself had a literal out loud laugh when the "monster" comes out to eat Jack. I feel like everything besides the weird cinematics of what someone else described as "hair eels" and the monster thing are really representative of a young infatuation. I don't even remember seeing Jack or Diane exchange names ever. Nor does Jack ever ask "what is up with all of the nosebleeds, vomit and passing out on bathroom floors?". Yet they find themselves together. For me, this feels like high school relationships. While disjointed and odd, the monster and hair eel bits feel like they are meant to be metaphors for what it feels like to know that maybe you're not quite "the norm" and to be afraid of it. I'm just guessing here. I really enjoyed this movie including the (I assume) unintended comedic bomb halfway through in the form of the monster. There is also the question of the twin sister and online porn film. I didn't really feel like she had a twin sister. I got the impression that she called Jack saying "I'm not gay" herself in some weird conflicted teenage angst thing. But conversely, if there really was a twin sister, couldn't Jack and her friend have assumed at first that it wasn't Diane getting the "shower"?