Will is an eighteen-year-old high school student known for his rebellious reputation. Raised by his grandmother after his mother left, he spends his free time working on his prized motorcycle and tutoring his classmate Josh in math. Beneath his tough exterior, he carries deep-seated guilt and struggles with depression, which he sometimes self-medicates. He dislikes rigid expectations and prefers to live day-by-day, though his connection with Rosie challenges his detached outlook.

Rosie is a focused, driven high school student determined to earn a place at Oxford University. She faces immense pressure to meet her mother's strict expectations regarding both her academics and physical appearance. To manage her anxiety, she privately engages in obsessive-compulsive checking routines and finds solace in writing music and poetry. Her predictable life plan is interrupted when she begins a secret, late-night correspondence with Will.

Josh is Rosie's sensitive twin brother. He receives math tutoring from Will White to prepare for his university entrance exams. As he finishes his high school years, he secretly struggles with his identity and his sexuality, fearing societal prejudice and the reactions of his parents. He relies heavily on the profound, unconditional bond he shares with his sister.

Simon is a solid, dependable university student who rows on the river near Rosie's college. He represents stability, safety, and comfort, offering a sharp contrast to the unpredictability of Rosie's earlier connections. He is practical and kind, though his traditional outlook sometimes prevents him from recognizing the deeper emotional struggles of those around him.

Mrs. Winters is an attorney and the demanding matriarch of the Winters family. She struggles with chronic, debilitating migraines while attempting to maintain rigorous order over her household. She places a high value on outward appearances and academic success, projecting her own rigid worldview onto her children. Her strict rules regarding diet and exercise significantly impact Rosie's mental health.

Gran is the dedicated grandmother and primary caregiver to Will and Amber. Having taken the children in after their mother left, she provides a stable, loving home. She is fiercely protective of Will but expects honesty and accountability, often challenging his self-destructive habits and substance use.

Amber is Will's younger sister. Despite the trauma of her early childhood, she maintains a grounded perspective and often serves as a voice of reason. She is observant and surprisingly wise for her age, quickly picking up on family tensions and Will's behavioral changes.

Marley is Rosie's vibrant and outgoing best friend. Unlike Rosie, Marley embraces adventure, rule-breaking, and spontaneity. She studies medicine and subverts societal expectations by chasing her own passions, serving as a confident foil to Rosie's constant anxiety.

Mr. Winters is the emotionally distant father of Rosie and Josh. He avoids conflict and largely defers to his wife's demanding presence in the household. He remains physically present at the dinner table but stays mentally detached from his children's personal lives.

Jen is a woman Will meets after moving away to work as a mechanic. She is perceptive and patient, attempting to build a genuine emotional connection with him, though she quickly recognizes that he harbors unresolved feelings from his past.

Darcy is a girl from Will's high school circle who engages in a casual, physical relationship with him. She seeks a more traditional boyfriend, which Will is unable and unwilling to provide.

Trevor is Marley's partner and the father of her children, representing the stable, happy domestic life that Marley successfully builds on her own terms.

Skye is Marley and Trevor's baby, representing the passage of time and the diverging life paths of the childhood friends.

Tom is a high school student who escorts Marley to the winter dance, briefly interrupting Rosie and Will's private moment outside.