Complex sentence: Zachary has not seen his father since his mother divorced him and moved back to the United States seventeen years ago when he was nine, but he agrees to go visit him when his half brother says he is needed in the trial.
Split into simpler sentences: Zachary has not seen his father since his mother divorced him and moved back to the United States seventeen years ago. However, he agrees to go visit Angus when his half brother says he is needed in the trial.