My Lee has slowly changed from a trusting guy, who believes that there is hope in Episodes 1 and 2, to a colder, more survival minded Lee at the end of Episode 3 and into Episode 4. My Lee always tried to calm things down between Kenny and Lilly, even though I thought one was right and the other wasn't, and he believed in humanity and hope. He trusted the St. Johns, and his downward spiral began when he helped kill Larry in the meat locker.
After killing Danny, he tried to hold onto his humanity by sparing Andy, not stealing the supplies, and shooting the girl in the street which strained his friendship with Kenny. After Carley died, my Lee left Lilly in the road and lost hope for the group. After Kat and Duck died, he pinned all his hopes on a boat just like Kenny and distanced himself from Chuck, Ben, Christa and Omid. Dropped Ben in the bell tower because he didn't think Ben could be saved, and wasn't willing to put his own morals over the group's safety. He tries to keep everyone elses' hopes up, but on the inside doesn't believe it when he says something positive and hopeful. He's lost the will to live, and only Clementine gives him a reason to keep going.