Ryle Kincaid's a neurosurgeon and Lily Bloom's main love interest after she moves to Boston, but labeling him just 'the boyfriend' misses the entire point of the book. He's the mechanism Colleen Hoover uses to explore the cycle of domestic abuse. At first, he's literally textbook perfect—charming, successful, obsessed with Lily in this intense, whirlwind way. Their initial chemistry is off the charts, which makes the first time he shoves her feel like a physical shock to the reader. His role is to be the 'good man' who does a terrible thing, over and over, forcing you (and Lily) to grapple with the reality that love and abuse can exist in the same person.
His backstory with the childhood gun incident is crucial—it's the supposed root of his 'angry moments,' this tragic flaw you're meant to sympathize with. But the novel slowly dismantles that excuse. His role shifts from dream guy to perpetrator, then to a pleading, manipulative figure who can't believe she'd actually leave. He represents the agonizing trap of 'but he's not like that all the time.' I finished the book feeling like I'd been put through an emotional wringer specifically because of how well his character was crafted to make you hope, again and again, that he'd change.