Does Hamlet really love Ophelia or is he toying with her affections?

From the beginning of the play, we see that Hamlet is not one to easily disguise the way he feels.  His melancholy over his father's death is obvious to everyone.  He tells Gertrude that he has "that within that 'passes show"  when she tells him to cast off his "nighted color."  In fact, Hamlet may decide to put an "antic disposition" on and fake madness after he sees the ghost in order to hide his intentions to avenge his father's death.  Hamlet may feel it necessary to take extreme measures to hide the way he feels.

And yet, if you study Hamlet's insane act carefully, you will find that the act itself is not entirely convincing.  He does little more than wittily and sarcastically reply to those around him--an act that only makes Claudius more suspicious. He has open disdain for Polonius; he reacts with anger and insults to the spying Rosencrantz and Guildenstern.  In other words, he is not one to feign how he feels toward others, even when he is acting-- or trying to act.

How does this discussion relate to Ophelia?  I don't think Hamlet is one to deceive or mislead.  His love letters to Ophelia are eloquent in their simplicity.  It is Polonius and Laertes who doubt Hamlet's sincere love toward Ophelia, and they underestimate both Ophelia and her relationship to Hamlet.  Polonius reasons that all young men are deceivers of women, and Laertes reasons that Hamlet's "will is not his own," and that his marriage will be a political one.  Both are wrong in hindsight.  Gertrude, for instance, at Ophelia's grave expressed her wish that she might have been Hamlet's wife. Evidently, she thought that Ophelia was a suitable marriage partner for Hamlet. Clearly, Hamlet was serious about Ophelia.

His reactions to her throughout the play are those of a hurt and rejected lover.  Remember that she broke off the relationship with him first.  His anger toward her reveal his pain.  At her death, Hamlet is inconsolate, but afterwards, he is able to obtain a maturity as well as a fatalism that he has not had before.

Hamlet loved Ophelia deeply.  He cannot express his love to her--not because of his unwillingness to do so, but because her siding with her father who is Claudius' ally prevents him from attempting to mend this relationship.  There is nothing Hamlet can do when Ophelia willingly takes part in a plot to spy on Hamlet and turns over his love letters to her father.  What we see throughout the play is the suffering of two young people who if not for the failures of their elders would have had a chance at happiness together.