Sasuke had never hated his brother. Even when he was nothing and Itachi was everything; when his mother would dote on Itachi and his father would never be quite as proud of Sasuke. Maybe it was Sasuke's eyes, even back then, that made the difference. Maybe Sasuke could see, if not understand. The kindness of his heart would not let him hate his brother.
To Itachi, Sasuke was the entire world. He was a fragile thing, the older brother, influenced so easily by responsibility, regard and expectations that he would strive to become more, to be the best at everything, drowning in conceit for everything that was granted to him. There was no bloodshed for the admiration, no pain for the love. What's free is cheap.
Sasuke was the world to Itachi. His smile, his heart, his painfully sharp beauty . Sasuke was his, and no one else's. He had no right to cheapen himself, to be so free with his affections. His brother was something people should earn. To even see Sasuke should be an honor granted to few.
Itachi always thought himself worthy of suffering more, to be more. He thought, 'a martyr is beautiful'. And nothing was ever quite as breathtakingly beautiful as Sasuke.
Always being the best, what was that worth without the pain that came with it? It made Itachi want to be hurt, defiled. He wanted to be his brother's tears, running down the smooth, pale and unmarked skin, wanted to be the tongue which would lick them off.
Itachi had always wanted to break. That's why he killed his lover, not to gain the Mangekyou, but to suffer through the pain and the guilt. And still it wasn't enough. The guilt was not even there when he really looked. Why was that? Why was he deprived of that fundamental human quality?
In the end, he'd killed his clan for Sasuke. For his only love. He told himself he'd be the world to Sasuke too, now. He told himself he'd make Sasuke the most beautiful thing in the entire world, a martyr. He told himself, 'I love you this much, my brother.'