His soul got damaged because he shoved half of his soul into Yuan Chu's body in the previous timeline after she died in his arms to anchor her soul back into her body when trying to figure out how to bring her back to life, it also allowed Yuan Chu to keep her memories of the first timeline when he turned back time. He was in love with her in TL1 but the cultivation technique he used in TL1 that he rejected in the current TL suppressed those emotions until he snapped when she died in his arms. The cursed mirror he used to rewind time affected his own memories but not Yuan Chu's, but half his soul literally being in her and the subconscious remnants of how broken he was when she died definitely have warped him into a yandere
