Severus Snape's heart had leapt the moment he saw the sweet girl of eight. She was cherubic and fiery and everything that was a Heaven from his home.
At eleven, they were Hogwarts students. Gryffindor and Slytherin, different as night and day. Snape thought of her as a best friend then. She made friends, but still kept to their promise.
Twelve years old, was a great year. Severus' and Lily's friendship grew. Their camaraderie might have been frowned upon, but neither cared. After all, they had each other.
Thirteen and hormones were flying. Severus realized that he might just fancy the petite redhead. She was nice to him, and that was a catalyst for his feelings.
Fourteen was a wonderful year. He still liked her a lot, but her friendship with him meant more than a romance. So, he let his desire slide and they remained platonic.
Fifteen hit the mark. That was the year he fell in love with her, and the year Potter started liking her. Potter didn't deserve the beautiful girl. He, Severus, was much better than him. He had genuine feelings for her, and Potter was an arrogant son of a bitch. The fact that the overconfident Don Juan had saved his life made his very incensed. That was the year Lily's and his friendship dissolved too. He fell in love with her loyalty to her friends and everything about her.
Sixteen was torture, he saw Potter grow and Lily slowly, but surely fall for him. Their friendship was over, and all hope for romance had been banished. She would never like him, as opposed to Potter.
Seventeen was slow, silent pain in itself. The moment he saw Lily and Potter holding hands, his heart broke into a thousand tiny pieces. That was the horrible year that they got married. Severus could feel the remains of his heart break further and further. Lily, his one true love, broke it.
And then she died.