Hamlet's feelings for Ophelia are rather ambiguous. His actions and words regarding her could be interpreted in any number of ways by an actor. Some actors play the scene as though Hamlet is truly contemptuous of Ophelia (and all women) as a result of his mother's hasty marriage to Claudius. Others interpret the scene as though Hamlet is secretly trying to warn Ophelia against being corrupted by the Danish court. In their view, he is not truly contemptuous—he hopes she can read between the lines of his feigned madness.
Going purely by the text, it is impossible to guess what Hamlet feels. One moment, he tells Ophelia,
I did love you once,
and then in his next line, he claims,
You should not have believed me; for virtue cannot so
inoculate our old stock, but we shall relish of it: I loved you
These opposing statements suggest madness, either feigned or real on Hamlet's part. He also rants about feminine use of cosmetics, linking make-up with dishonesty. In his rant, he advises Ophelia never to marry so as to avoid sin and corruption. Some argue that his advising Ophelia to "get thee to a nunnery" is meant to be double-edged.Even if it involves rejecting Ophelia, Hamlet is expressing his hope that she will escape the bad influence of the court and sexuality in general.
However, even if Hamlet is feigning insanity in this scene, his words do little to throw Claudius off his trail. He is only hurting someone he loves on some level. It might be most accurate to say he may or may not have loved Ophelia in the past. Ophelia's description of his previous wooing of her and Hamlet's later lamentations regarding Ophelia's death suggest his romantic interest was genuine. Once again, it all comes down to how the actor playing Hamlet sees the character. However, during this conversation, he is arguably projecting his anger towards his mother and the world in general onto the innocent Ophelia. His ramblings about marriage, virtue, and dishonesty are consistent with his complaints against Gertrude. One might conclude that while act 3, scene 1 does not give conclusive evidence as to whether or not Hamlet loves Ophelia, it illuminates more about his feelings towards Gertrude and women in general.