Therein lies the rub. I think unfortunately that #4 is actually correct. Part of the tragedy of this play is the fact that when Hamlet met the Ghost and was set on his path of unswerving revenge, that meant there was no space in his life for romance or love, like other youths of this age were doing. I do believe he did love Ophelia, and we see in Act V scene 1 honesty emerging from his intense frustration and anger that he was not able to pursue that relationship in the way that he wanted.
Consider Hamlet as if he was two different characters. The Hamlet before he found out about his mother, Claudius, and then his father's murder, and the Hamlet after all of these things became known. The young man who went away to study, no doubt, loved Ophelia. His notes and gifts are evidence of a passion. However, after his father's death, his mother's remarriage, and then the news of his father's murder, Hamlet changed. The young man who innocently loved was no more, and he no longer had room in his life or his emotions for a love affair.
I'm with lmetcalf all the way on this one. Hamlet does some things to protect her (acts kind of crazy, tells her to go away and to keep her father at home), but he doesn't tell her why or really make sure she listens to and follows his warnings, unfortunately. The result is that she is distraught enough to take her own life. When he discovers it's Ophelia's grave the clowns are digging, something kind of snaps in him. It seems to me he's never really the same after he hears that news. He appearsresigned to play out whatever Claudius and Laertes have in store for him, and I'm sure part of that is his feeling responsible for his part in Ophelia's death.
I think he is speaking the truth. He may have been frustrated or disappointed in her going along with her father in her pushing Hamlet away and her going along with Polonius and Claudius when they are in hiding and spying on Hamlet and Ophelia to determine if Hamlet's changed behavior is a result of Ophelia, but in the end he did love her. He is so caught up in trying to prove Claudius's guilt that he just can't be true with Ophelia.
In the graveyard scene when he realizes that the grave is for Ophelia he goes truly a bit crazy. He starts to grapple with Laertes in the grave! He seems to be in a sort of fight with Laertes over who loved Ophelia more, and he says he "will fight with him upon this theme." When the Queen questions him, he responds, "I loved Ophelia. Forty thousand brothers could not (with all their quanity of love) make up my sum." These words should be taken with sincerity; Hamlet doesn't really have anything to gain in their being lies. The actions and the speech actually make Laertes more angry than he was, so it isn't as if the speech is only to calm Laertes and trick Claudius in some way. Claudius actually has to bring Laertes to a restrained state. Hamlet tends to hate extreme emotionality (remember his caution to the actors not to "over-act) so this extreme display of emotion must reflect the almost instinctual response by Hamlet upon realizing thathe truly did love Ophelia and now it is all too late and she is dead.