Complex sentence: Devastated that his father has sent Shu Nian away, Xie Yan's relationship with his father sours, particularly since the older Xie already knew about the relationship between Xie Yan and Shu Nian.
Split into simpler sentences: Devastated that his father send Shu Nian away, Xie Yan's relationship with his father soured. Since the older Xie already knew the relationship between Xie Yan and Shu Nian.