How we cite our quotes:
Losing your best friend sucks, even if it's only for three months and two days. (1.3)
The only way "friendship" could be a more obvious theme is if it were on the cover. Losing Peris is such a serious issue that Tally keeps track of the days (and probably the hours too) until she'll see him again. Notice also how this quote sets us up for the idea of "losing" friends because of the surgery.
"Wow, that's crazy. Your boyfriend or something?"
Tally shook her head. Peris had gone with other girls, and Tally had dealt with it and tried to do the same, but their friendship had always been the main thing in both their lives. Not anymore, apparently. (3.62-3)
Friendship in this book can overlap with other relationships—like boyfriends and frenemies. But, do you buy it when Tally says she's just friends with Peris? Notice the comment that she "had dealt with it" when Peris dated other girls. Does that sound like she has something more than friendly feelings?
Peris had been so pretty, and grown-up looking, and he'd said they'd be friends again. Once Tally was pretty too... "Basically, it sucked," she said. (3.66)
Here's a rule of thumb: if a friend says "I'll like you more once you're pretty," that might not be the best friendship. (Also, check out when Tally asks Peris if they're still friends, and he says, "Sure," which is not an enthusiastic response [2.97].)