What’s the theme?

One important theme in the novel is th nature of friendship. Will begins the narrative comfortably attached to the friendships he shares with Mi Su and BT. They are, in many ways, the most stable and trustworthy parts of his life (particularly when the unpredictable volatility and frustrating peskiness of his sister, and his parents' passivity in response to her, are taken into account). Over the course of the narrative, however, the stability of the three-way friendship is tested by a couple of factors - Will's growing frustration with BT's apparent passivity, Mi Su's apparent indulgence of that passivity, by his growing feelings of attraction for Mi Su. Ultimately, though, the biggest challenge to that friendship comes after Will sees Mi Su and BT kissing, a situation he experiences as a breach of trust and respect on both their parts. That breach is to some degree healed when Mi Su reacts with compassion to Will's expression of his feelings towards her and his reactions when he perceives those feelings as not returned. The biggest healing of the breach comes when both Mi Su and BT reach out to Will and his family in the aftermath of Tabby's accident, their actions revealing that their feelings for him run more deeply and rely on a more fundamental human respect and connection than simply playing Monopoly and eating pizza. Here, the novel is apparently making the thematic suggestion that genuine friendship has less to do with what one does with one's friends, and even less to do with how friends feel about you when times are good. The true nature of friendship, the novel contends, is indicated by the reactions of friends in times of difficulty, challenge, and stress.