The thesis statement you write depends upon whether or not you believe that Hamlet, in Shakespeare's play by the same name, is in love with Ophelia or not.
There is a great deal to consider. Is Hamlet insane? Did he really see the ghost of his murdered father? Did he ever love Ophelia? Is it possible that he could love Ophelia at all in that he is a prince?
You may recall that Laertes (when he prepares to leave the castle) warns Ophelia about trusting Hamlet: that he will use her and throw her aside:
He may not, as unvalued persons do,
Carve for himself; for on his choice depends
The safety and health of this whole state... (I.iii.22-24)
Laertes tells his sister that Hamlet could never marry her because she is not highly born enough to marry a prince and that Hamlet must always have the affairs of Denmark foremost in his mind. Of course, Hamlet is not a young man who plays by the rules: and he is a prince! And Laertes proves later to be hot-headed and a poor judge of character is throwing in his lot with Claudius, a king who married his brother's widow within months of Old Hamlet's death—seen as an incestuous act by the Elizabethans.
Hamlet is also pretty savvy. He knows Claudius, Gertrude and Polonius are watching him. He is aware that Ophelia is spying for them: but in her defense, what would a girl whose father works for the King do when asked to keep an eye on Hamlet, especially if they say it is for his own good?
Hamlet becomes angry with Ophelia. He asks her if he can trust her...is she honest and truthful:
Ha, ha! Are you honest?...Are you fair? (III.i.112, 114)
Ophelia says she is. She tries to return his gifts, but he rejects them, saying he never gave them to her. But she disagrees: not only did he give them, but also with sweet words.
He tells her he loved her, and when she says she believed he did, he says he never loved her. He tells her to join a convent and never have children. He is unkind and cruel. Ophelia has not betrayed him and does not understand, but looks to perhaps an addled mind for the cause, which is inferred by others due to Hamlet's father's death...and perhaps even his mother's "o'erhasty" remarriage.
However, Hamlet is collecting information to expose his uncle for the murderer he is.
When Ophelia dies (some say suicide, but I believe in her eventual madness she did not realize what was happening, as Gertrude reports), Hamlet is devastated. He even goes so far as to jump into Ophelia's grave and fights with Laertes, her brother. In Act Five, scene one, Hamlet rages at Laertes:
I loved Ophelia. Forty thousand brothers
Could not, with all their quantity of love,
Make up my sum. (270-272)
Hamlet tells Laertes that no brother could love Ophelia like he loved her. Gertrude had even hoped Ophelia and Hamlet would marry: and if the Queen felt so, it is not hard to imagine that their relationship was real and favored by Hamlet's mother—perhaps even his dead father.
So your thesis statement depends upon what you believe. If you feel that Hamlet was using Ophelia only to throw her away when he was done, you would write a statement stating something to that effect, with information from Laertes' speech to support your statement.
If you believe Hamlet was hurt, thinking she had betrayed him but never stopped loving her, you would write your statement to that effect and look to his behavior at her funeral. For if he did not love her, why was he so hurt?