The narrator was fine for the main character and for Leone but was terrible for the other voices (Jamie, the badminton friends, Sean, the moms, etc). The book had some weird presumably Australian-isms. 
The prose is partly weird because it’s an Australian author writing a book set in the us without someone picking out all the weird turns of phrase that these people would never say. (“Singlet”, “trash our rubbish”, “salami pizza”) The other thing that’s getting to me is that it’s 3rd person, but the kind with insight only into one persons thoughts, but the narration says things about the POV character that he’d clearly never think like “…letting his dimples come out to play”. It’s one thing for the POV character to be obsessed with the love interest’s dimples but it’s weird for the prose to be obsessed with the POV character’s dimples.
In what world do basically stranger roommates cook all meals and do laundry for each other right away? In what world is a gay guy not even a little scared for his safety to kiss his either straight or deeply closeted roommate? When was this supposed to be set (who brings their music to the roller rink on a thumb drive? Leone is taking taxis not Ubers or Lyfts?) In what world does Theo not have any concern about “am I gay? Does this make me gay?”