Mu Yuan and Jack's friend had an unpleasant experience. When they were dating, he had once met one of Jack's friends. He was a straight man and could not accept the things between Jack and mu Yuan.
Jack did not bring his friend to meet mu Yuan on purpose. It was just that while they were on a mission, his friend had noticed something. He was a straightforward person with a fiery temper. He did not say anything explicitly, but he had some evil thoughts during the mission and wanted mu Yuan to die.
He told mu Yuan that as long as he was dead, Jack would not do anything wrong and would not be stubborn. That mission was separate. Jack was with another United Nations Army, and mu Yuan was on the other side. He was plotted against by Jack's friends and was in prison. It was him who was calm in the face of danger and solved the crisis by planting flowers into trees.