This is all after Michael and Walt leave in the boat Ben gave them, and back in New York. (I am trying to find the episode you are looking for) This is from Lostpedia:
Racked with guilt over his murder of Libby and Ana Lucia, Michael attempts to kill himself by driving his car into a wall. Michael wakes up in the hospital and Libby enters, however this appears to be just a dream. Michael wakes up again and a nurse enters and offers to call Walt, saying that Michael had a note taped to his chest addressed to Walt.

Sometime later, Michael goes to his mother's house, who is caring for Walt. Michael's mom doesn't understand how her son came to survive the plane crash two months ago and return to the mainland. She also does not know why Walt is so distraught. Michael leaves her and goes to a pawn shop where he sells Jin's Rolex watch in exchange for a gun.


In a back alley, he is preparing to shoot himself when Tom approaches him. He tells him that he has a job for him, and realizes that the reason Walt won't see him is because Michael told him he killed Anna Lucia and Libby. Tom also informs Michael that Michael cannot kill himself even if he wanted to. Michael returns to a motel room and tries to shoot himself in the head, but the gun refuses to fire. Suddenly, a news report comes on TV announcing that the wreckage of Oceanic 815 has been found at the bottom of a trench in the ocean. Michael heads to Tom's hotel room where he finds him in the company of another man. Tom informs Michael that he will pose as a deck hand named Kevin Johnson on board the freighter, a ship commissioned by Charles Widmore, sailing out of Fiji. Michael reads the message "not yet"

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