Because he is such a tragic and beautiful character. Mello is intelligent, insightful, and well-spoken, but sadly, when he lets his brash and obsessive side get the best of him, bad things happen. His entire life and the path that it went down is very saddening. I can't help but feel a little bit angry with Near for not having done something about it when he knew how to help Mello and knew that they could have been friends. Or maybe...he knew that Mello had to discover that on his own, and would only be resentful about it if Near approached him with the matter. He was wonderful, his mind and self, but sadly let the imaginary game of becoming L and defeating Near consume him, leading to the distortion of himself. That's quite similar to what happened with Light being Kira and trying to defeat L, actually. No, it's EXACTLY similar. The only difference being that Mello did not become eaten by a pure evil, and did not have personality similar to Light's. And in the end, he realized in his heart that defeating Kira was all that truly mattered, and that it wasn't a game. The scene where he gave Near information about the notebook was very touching, and goes to show that they really could have had a great friendship. You see, Mello and Near can be two different sides of L. L, with both of those sides, tends to be able to do those things on his own. However, when the sides are split, their powers can't prevail alone. Thus, when Near said that together they could surpass L and defeat Kira. Mello, you will forever be in my heart. <3