Sebastian, Charles’s first love, is a tragic figure who spends most of his life trying to escape adulthood and responsibility. As a youth, Sebastian possesses an exuberance and innate understanding of beauty that charms everyone around him. However, he also displays a whimsical childishness, carrying around his teddy bear, Aloysius. He uses Aloysius to avoid subjects that distress him or to diffuse tension, escaping back into childhood. He associates youth with joy and age with sorrow, foreshadowing his grim future. He encapsulates his desire to forever avoid consequences when he tells Charles he prays for God to make him good “but not yet.” Sebastian recognizes he must someday take responsibility for his actions but wants to procrastinate indefinitely. Eventually, he turns to alcohol for escape. Instead of being charmingly eccentric, his childishness becomes a dangerous disregard for the consequences of his actions. Sebastian drives drunk, steals from friends, and manipulates Charles into giving him money. His alcoholism leads him to live in self-imposed exile from his family and causes his health to deteriorate. Nevertheless, Sebastian finds his way back to his family’s Catholicism and becomes an underporter at a Tunisian monastery, symbolizing the unconditionality of God’s love.
Sebastian’s desire to care for and guide someone informs his character arc. His first charge is Aloysius, whom Sebastian fusses over. In his early relationship with Charles, Sebastian acts as the leader in their escapades, teaching Charles about beauty beyond Oxford society. However, Sebastian rejects Charles once the power in their relationship shifts. As Charles matures, finding a career path through art, Sebastian flounders, turning to drink. Even though Charles tries to appease Sebastian by giving him money for alcohol and siding with him against Lady Marchmain, Sebastian recognizes that Charles now cares for him, not the other way around. In the depths of his alcoholism, Sebastian finds comfort in the fact that Kurt, pathetic and without resources, will always require someone to guide him through life. After Kurt’s death, Sebastian realizes that he can turn his desire to nurture toward spiritual purposes and tries to become a missionary. Although too ill to accomplish this goal, he still gets to offer care to the monastery buildings, helping the monks there carry out their spiritual work.