1) The only other options are Sasuke, an angsty emo who loves nobody, and Naruto, who, while he cares for Sakura, is obnoxious and immature. Lee, on the other hand, is always there for Sakura, protecting her and doing anything for her. When Lee and Sakura met, almost the first thing Lee said to her was, "I promise to protect you with my life." And he has proven, several times over, that he meant it.
2) Lee is a hardworking, committed, and really very sweet character. He is smitten with Sakura, and a lot of people feel that he deserves her.
3) Sakura obviously cares for Lee as a good friend, and treats him as such on numerous occasions. There is definitely something between them, friendship at the very least. It could potentially blossom (or cherry blossom, pun intended) into something more romantic.
I know, right?? Lee DESERVES her!!