Why, she would hang on him as if increase of appetite had grown..... Frailty, thy name is woman!
Act II: Scene II
I have of late.... lost all my mirth, forgone all custom of exercises...
My lord, we were sent for.
Act II: Scene I
Get thee to a nunnery. Why wouldst thou be a breeder of sinners?
In this scene, Hamlet is out of place of the new king's court. He believes that his mother marrying his father's brother was wrong and she was not properly mourning him. This was the start of Hamlet's downfall.
Rosencrantz and Guildenstern were ordered by Claudius to check in on Hamlet and see what his odd behavior was about. Hamlet tells them that he had lost all his joy and everything to him appears bleak and worthless. This represents how his view of the world has changed drastically after the death of his father and the wedded union of his mother and his uncle.
Hamlet tells Ophelia that he does not love her anymore and that she should go to a nunnery so she does not become a "breeder of sinners". The scene represents how Hamlet's goal of killing his uncle has changed him for the worse.