To plan an effective response to this question it is important not just to consider the textual evidence that could be used to support the idea that Hamlet did love Ophelia, but also to consider and explain the sections of the play that suggest he did not actually love her, such as the famous "nunnery" scene in Act III scene 1 when Hamlet rails against Ophelia and curses her. This of course seems completely out of character when his words in Act V scene 1 are considered, when he discovers that the funeral he is watching is that of Ophelia:
I loved Ophelia. Forty thousand brothers
Could not with all their quantity of love
Make up my sum.
These words seem unequivocable, and can be usefully referred to as evidence that Hamlet did love Ophelia. It is therefore important to explore why Hamlet said what he did to Ophelia in Act III scene 1. It is possible to argue that Hamlet insulted and cursed Ophelia because he became aware during the course of their conversation that they were being spied upon and also that Ophelia was being used by her father and Claudius to turn against him and betray him. This is why he responded in such a vitrolic way to her: not only do his words express the pain of betrayal but also the intense disappointment he feels at discovering that he has been betrayed by yet another person whom he loves. This is certainly how Hamlet is played in Kenneth Brannagh's film version of the play. Hamlet's love for Ophelia could therefore be described as constant throughout the entire play, but it is his anger and emotions that explain why at times he appears to hate her. A good thesis statement you could use to support this argument therefore might be:
Hamlet in Hamlet remains constant throughout the play in his love for Ophelia. However, the discovery of Ophelia working with her father and Claudius against Hamlet and the awareness of the attention that Claudius pays to his relationship with Ophelia makes him deliberately appear to contradict his emotions.
Such a thesis statement would allow you to argue the case as expressed above, exploring other quotes that could be used to indicate Hamlet loves Ophelia, and also other instances where the reverse could be argued.