Star Wars continues to flesh out Kylo Ren's story in some pretty major ways, effectively retconning his depiction in the sequel trilogy. By the end of the sequels, Ben Solo is redeemed before giving his life to save Rey. However, the true nature of Kylo Ren's dark side corruption is pretty different from how it's shown in the movies alone.
Beyond the sequels, Kylo Ren's story has primarily been revealed in two graphic novels: 2019's The Rise of Kylo Ren by Charles Soule and the currently ongoing Legacy of Vader series (also by Soule). In both stories, readers are shown the truth behind Kylo Ren's dark side corruption, and the results are as revealing as they are tragic.
Star Wars' Newest Kylo Ren Story Changes How We See Ben Solo
In Marvel's new and canonical Legacy of Vad