Shane died because of a violent confrontation with Rick. Their relationship had deteriorated, and it all came to a head in a fatal encounter. Rick felt he had no choice but to take Shane out to protect himself and the group.
Definitely. Rick kills Shane because of the escalating tensions and conflicts between them. Shane becomes a threat to Rick and the group, leading to the fatal encounter.
Shane's death in the Walking Dead comic occurred after a series of conflicts with Rick. Rick, seeing no other option, took the fatal shot. This was a turning point that changed the dynamics within the group.