The Hamlet who is talking to Ophelia is not the same Hamlet that she fell in love with, he had been hurt by her father who had killed his father. That changed him immensely which changed his feelings for her. It saddens the audience to see that Ophelia continues to love Hamlet despite his mistreatment of her. Ophelia’s tragedy continues, as she never gets to hear for herself Hamlet’s true feelings. His meeting with Ophelia immediately follows his “to be or not to be” monologue, which was about Hamlet’s suicidal thoughts. So he knows that if he does something, if he acts, if he kills the King, he will take serious risks and may die in the attempt. If he chooses not to act, he will lose his self-esteem. Whatever he chooses, he will not be fit
