Why was Lot afraid to escape to the mountains?
Rashi: He was afraid that his rescue from S'dom was due to the fact that, compared to the people of S'dom, Hakadosh-Baruch-Hu considered him a Tzadik, 1 but that, once he arrived in the vicinity of Avraham, he would be considered a Rasha, and he would suffer 2 the same fate as the Sedomians. 3
Mishnas R. Aharon 1 p.149: Before, Lot went with Avraham and was not harmed! Now that he sees that he is saved in Avraham's merit, surely he will learn from him and be a total Tzadik! Rather, there is great ruin in separating from Torah. Once Lot separated from Avraham, "the crooked cannot be fixed." He cannot be Avraham's Talmid like before.