It's only been a week in show time since his wife died. His son had to shoot her. Members of his group are dying; he's not sleeping well, under constant stress and having to put aside this major traumatic loss in his life which, for some reason, he feels responsible because he didn't reconcile with the disloyal thing. How quickly can a person bounce back? There's the crushing guilt for killing Shane as well. Personally I think Rick deserved better friends and family but for some reason the character loved them.
More people would probably be like Rick in that situation than be "normal."