from HP6, p. 449, in the common room, you'll see
"I love you, Hermione," said Ron, sinking back in his chair, rubbing his eyes wearily.
Not until after the words had left his mouth did Ron realize how true these words were. Although he was sure Hermione would not take the words how he truly meant them, he couldn't help blushing deeply.
Looking back, Ron realized that it was in his second year that he thought of Hermione as more than his know-it-all friend. As Hermione lay petrified in the hospital wing, Ron found himself regretting all the unkind things he had ever said to her. It was terrifying to the twelve-year-old boy to think she would never wake up. She, from that moment on, became his first crush.
While Ron was determined to keep his feelings a secret, it became harder as he and Hermione got older. In their third year, Ron couldn't help admiring her as she slapped Malfoy round the face and showed true bravery and strength in saving a friend. Thus, his crush intensified.
As they entered their fourth year, the Triwizard Tournament began, and with it came drama in the form of the international Quidditch player Viktor Krum. Ron was struck dumb when he discovered that Hermione was Krum's date to the Yule Ball. Ron was so narrow-minded that he thought no one else would ask her, and that he himself was the only one who appreciated her intelligence and growing good looks. Still determined not to reveal his feelings, he blamed his surliness on Hermione's "fraternizing with the enemy." Even though it further strained his relationship with Hermione, his feelings were still a secret, and that was all that mattered to Ron at the moment.
Then, with fifth year, came all of the hormones of two fifteen-year-olds. Ron sat on the sidelines as Hermione continued her confusing relationship with Krum, and Harry began his relationship with Cho. Just as he thought his chances with Hermione were less than zero, she gave him a kiss that penetrated his very soul. Even though he was sure it was only a friendly gesture (because she had given Harry the same kiss at the end of last year), and he was sure it was purely for good luck, he couldn't help but melt as her lips touched his cheek. Once again determined to hide his feelings, he said nothing, and played his best in the Quidditch game.
Finally, and most recently, came sixth year. Although Ron did not want to like Hermione, the fact was that he did. And as he reassessed his feelings for Hermione when she arrived at the Burrow that summer, he realized that he had grown beyond a crush, and was completely in love with Hermione. Then, the fateful Herbology lesson took place, and Ron was almost positive the Hermione liked, or possibly even loved, him back. Ron was on cloud nine, yet he kept his elation to a minimum, because he still valued her friendship. But then, Ginny touched a nerve and spoke a horrible truth that Ron could not get over.
She said something that resonated so strongly with Ron that he could not say another word: "Hermione snogged Krum." Ron felt like he had been betrayed. He felt like he had had something snatched away from him that he could never get back. He began to treat Hermione as he would his worst enemy. He felt horrible for doing it, but he thought it was necessary. She needed to feel as he felt.
And then came Lavender Brown. She seemed eager to throw herself at him, and he needed to cause as much pain to Hermione as possible. So, whenever Hermione came near, he grabbed Lavender and began to kiss her ferociously. Hermione became as distant as ever.
Then, something happened that Ron could never have predicted--he was poisoned. While he was unconscious, he heard snippets of conversation. He had a hard time judging what was his imagination or real as he slipped in and out of his dreams. In these dreams, he was chasing down an indignant Hermione, who refused to speak to him. For the first time, he heard her voice and tried to call after her. He ended up saying, very weakly, "Er-my-nee." He attempted to apologize to her and tell her how much he was in love with her, yet he never heard her again.
Once he had returned to full consciousness, he found that Hermione had been at his bedside, almost constantly, and he had a fleeting fantasy of Hermione confessing her love for him as he lay there. But the best thing that came out of this was that he was speaking to Hermione again. Ron realized how horrible he had been towards her and avoided Lavender at all costs. He loved Hermione, not Lavender, and owed her nothing.
His thoughts returning to the present, Ron was paying attention enough to her Hermione's response, "Don't let Lavender hear you saying that." Ron also noticed that she had gone very slightly pink.
Ron smiled, and hoped her blushing meant what he thought it meant: that she reciprocated his sentiment; that she loved him, too.