So, I personally don't like the idea that Ginny gave Harry a love potion to make him fall in love with her, but this theories is slightly different.

I personally think that she did give him a potion, but that it didn't work, I'll explain later. If she did, it would have been the same one Romilda Vane attempted to give Harry. I think it would probably works by making the drinker fall in love with whoever they see next, so you could say in the movie, The Half-Blood Prince, when Ginny gives Harry a bun, their looking directly into each others eyes, and it looked to me like Ginny was a bit disappointed. But, why didn't Harry react the same way Ron did when he took it. Well, what if the potion doesn't work if the drinker see's someone they already love, so the effect don't work.

Another theory is that Harry always suppressed his love, unlike Ron, so he took these new emotions and hid them.

Please tell me what you think, I personally prefer the idea that Ginny did give Harry a love potion, but he already liked her.