Answer:
his love for Ophelia being rejected
Step-by-step explanation:
According to the book Hamlet, after Hamlet goes 'mad', different people have their opinions on why he lost his mind.
Polonius suggests that Hamlet's madness stems from the fact that Ophelia rejected his love, but he was wrong.
Hamlet was not mad, but was merely feigning madness so that Claudius would not get suspicious of his plans.