Why was Reuven not present when they sold Yosef? Where had he been?
Rashi #1: It was Reuven's turn to serve his father that day.
Malbim: Reuven was with the other brothers, away from Yosef. He intended to go to save him before the Yishme'elim arrived; Hashem sent Midyanim to take Yosef before Reuven got there.
Targum Yonasan: In fact, he hoped that, if he returned Yosef to his father, he would forgive him for his sin.
Oznayim la'Torah (citing Pirkei d'R. Eliezer): Reuven went to meditate on one of the local mountains, with the intention of returning in the night to extricate Yosef from the pit and return him to his father. See Oznayim la'Torah DH 'Vayashav Reuven' #3.
Why did Reuven rent his clothes?