Love is an astounding thing. Always have, always will be. It is usually the driving force behind so many different actions for so many different people.
For Ron Weasley, love has taken the form of sacrifice.
Oh yes, for while an outsider might observe him a cruel heartless boy who lashed out at her and hurt her with absolutely no care at all, with no regrets; who saw their friendship as trying to force a cat and a dog who always hated and chased each other to actually sit together in the same place for a whole day without one single fight, insiders knew all of their arguments for what they really were. Some might say that all these arguments result from all the underlying sexual tension between the two teens, and that may be partially true, but the real reason was that both Ron and Hermione thrive the challenge.
Ron loves to press her buttons. She loves the way his face would heat up and turn scarlet as he tried to get his point across. He loved how chocolate brown eyes filled with fire and passion as she contradicted him in the loudest way possible.
She was the sugar to his tea, the colors to his life, the only person who made his life enjoyable and worth living.
So he did not spare a moment to think about it as he ran to stand at her side that night. He regretted nothing when he jumped in front of her, when he defended her. As he lay on the ground, his robes being soaked through by blood and pain racking his body, the only thing on his mind was her. When he opened his eyes to her beautiful face, tears streaming down it and words that were not heard coming rapidly through her lips, he broke into a weak smile. It did not matter what happened to him, how much pain he was in, what matters is only one thing.
I saved her
As the pain started to fade, and he became more and more detached from the world around him, he knew he only had one last chance to tell her. She had to know that he regretted nothing, and that he would die for her a thousand times if he had to. He wanted her to know every single thought he ever had about her. How beautiful she was, how she was and will always be the only person who he would ever want. He wanted to say so many things, to say a million word to her.
He fumbled for her hand, and with the very last breath inside him, he managed to tell her everything in just three words.
"I love you"