Ophelia is a young woman caught up in a situation far beyond her control. She loves Hamlet, but she also wants to obey her father and her brother, and they regard her only as a maiden who needs their constant guidance. They warn Ophelia that Hamlet is only using her, that he doesn't really love her and will never marry her. He will only take advantage of her and ruin her.
Ophelia's own father, Polonius, decides to use her to try to try to determined why Hamlet has gone crazy. Ophelia returns Hamlet's letters and renounces their relationship. Hamlet, who is actually only pretending to be insane, is hurt by what he perceives as Ophelia's betrayal, and he becomes cruel to her, insulting her with plenty of sexual innuendos. Later, he accidentally kills Polonius.
Ophelia cannot take any more. She has been pulled one way and then another by people who claim to love her but actually treat her horribly. She can no longer cope with her family's control, her father's death, and Hamlet's anger, and she goes crazy for real. Her mind becomes overwhelmed and unhinged, and she has no one to which to turn for help. Her father is gone. Her brother is bent on revenge. Hamlet is out of control. Ophelia is abandoned, left to herself, and finally, she kills herself in desperation. Indeed, Ophelia is probably the most tragic character in this tragic play, for she is the most manipulated, least supported, and arguably most fragile.