The Redemption of Time Baoshu

In the midst of an interstellar war, Yun Tianming found himself on the front lines. Riddled with cancer, he chose to end his life, only to find himself flash frozen and launched into space where the Trisolaran First Fleet awaited. Captured and tortured beyond endurance for decades, Yun eventually succumbed to helping the aliens subjugate humanity in order to save Earth from complete destruction.