Susannah is the primary love interest of the novel, but unlike Lucy, she is unconcerned with how Crossmore might view a lesbian romance. Initially, Susannah is just another girl in Lucy’s friend group, and her mixed attitudes toward Lucy are confusing. As Lucy and Susannah grow closer, however, Susannah makes it clear that she is as in love with Lucy as Lucy is with her. While Lucy’s family is poor and close-knit, Susannah’s only real relative is Catriona, her mother, since her father has a separate family in the city and her brothers moved away from Crossmore. These loose connections and wealth allow Susannah greater freedom than Lucy, who risks poverty and exclusion if her sexuality is exposed. Susannah is a much more sexual character than Lucy, who does not use her sexuality except in response to Susannah. Susannah is willing to flirt with boys to get what she wants, and she even uses the threat of sexuality to lash out against her mother. Lucy often fears that Susannah is using her in a similar manner, but Susannah’s own expressions of love indicate a sincere desire to be with only Lucy.

Lucy’s idolization of Susannah is often in conflict with Susannah’s actual characterization in the text, making it so that there are effectively two Susannahs in Sunburn. One Susannah is the divine, perfect version of Susannah that Lucy obsesses over, who can do no wrong and must be worshipped unconditionally. This idealized Susannah is not real and exists only as a crystallized image in Lucy’s mind. The real Susannah is a full and complex person with her own concerns, desires, and motivations. A moment of revelation for Lucy is when Susannah claims that Lucy has all the power in their relationship since Susannah, too, sees an idolized version of Lucy in her mind. The contrast between these two versions of Susannah is a central issue in the text, as Lucy struggles to reconcile the perfection of her relationship with Susannah in private with the necessity of living openly to fulfill both of their desires. Living openly is a critical part of Susannah’s motivations, which informs her behavior after leaving Crossmore. Susannah’s travels throughout Central and South America serve as a representation of self-exploration, which Lucy, in contrast, resists.

Martin is Lucy’s childhood best friend, and he serves as a secondary romantic interest. Martin’s status as a romantic interest is debatable, however, because Lucy makes it clear that she does not have a romantic love for Martin. Nonetheless, the framing of the novel sets up Lucy’s choice as between being in a relationship with Martin or Susannah, and Lucy does occasionally admit that she can see herself being happy with Martin, even if that life would be inauthentic. Martin is a critical character in Lucy’s story because he represents the heteronormative life that Lucy could have had if, as she says, she were a different person. Throughout the novel, Lucy notes that in another universe, she would fall in love with Martin, and they would grow into a relationship, get married, have children, and grow into old age much like their parents did. However, Lucy does not genuinely feel the attraction to Martin that everyone expects her to.

Much like Susannah, there are two Martins in the text. One Martin is a stereotypical, rural boy from Crossmore who likes Lucy because he is supposed to like her, wants to be with Lucy because everyone assumes he will, and could never accept Lucy as a lesbian because it would conflict with his rigid worldview. The other Martin, which is a more accurate reflection of his character, is open-minded and accepting; he loves Lucy for who she is, not for who she is supposed to be. In the final chapters, Martin shows this side of himself most clearly by accepting that Lucy is in love with Susannah. Likewise, his patience and willingness to stand by Lucy throughout the novel show that he is a good friend above all else. Still, Martin is attracted to Lucy, and this attraction creates a tension between them that cannot get resolved without Lucy’s honesty. In this respect, Lucy sees Martin as a tool she can use to both experiment with a heteronormative lifestyle and convince others of her own “normalcy.

“The girls” refers to the group of girls that Susannah and Lucy hang out with in high school. The group consists of Maria, Joan, Bernadette, Eimear, and Patricia, though Patricia is considered an outlier of the group. Maria is effectively the leader of the group, and the girls all look up to her, which Lucy attributes to the fact that Maria is the youngest of seven sisters. Her older sisters give her an added layer of social and cultural knowledge and wisdom, which the other girls envy. Joan is close to Lucy but, much like Martin, seems to be a friend whom Lucy does not fully understand. Eimear and Bernadette are the most “normal” of the group, mostly concerning themselves with gossip and boys, while also enforcing these norms on the group by consistently seeking approval and asking about romance and rumors. Patricia is an outlier because she has the most disruptive home life, though her ostracization is also due to her bad attitude. Lucy, specifically, cannot stand Patricia, though Susannah is close with Patricia before beginning a romance with Lucy.

The girls serve as the main method of social reinforcement in the novel. They discuss the other teenagers in Crossmore, and Lucy describes this gossip as “vicious.” They criticize girls who have sex too soon or too often, poke fun at girls who make mistakes, and defend each other by tearing down their rivals, such as Rita. Most importantly, the girls are not accepting of gay and lesbian people and relationships, a point that Susannah deliberately provokes to show Lucy how little these friendships mean. Lucy places a great deal of value on her friendships because they shape who she is, but Susannah is willing to cut out all the girls if it means that she can live openly. In the end, Susannah confesses her sexuality to Maria, who concludes that Susannah and Lucy are lesbians, which she then spreads over town, showing how their friendship cannot stand in the way of Maria’s desire to ostracize others and reaffirm her own normalcy.