Complex sentence: Sinclair later told his son, David, that around Sinclair's 16th year, he decided not to have anything to do with his mother, staying away from her for 35 years because an argument would start if they met.
Split into simpler sentences: Sinclair later told his son, David, that around Sinclair's 16th year, he decided not to have anything to do with her. He stayed away from her for 35 years because an argument would start if they met.