Romeo and Juliet

I am writing an essay comparing and contrasting two characters from Shakespeare's Romeo and Juliet. I want to write about Romeo and Mercutio, but I can't find a correct adjective to describe Romeo. Romeo was in a very emotional state when he first fell in love with Rosaline, and said that she was the most beautiful woman who ever lived since the Earth began, and that there is no one prettier then her. When Rosaline said she didn't like him, he became even more emotional and cried every morning, locking himself in his room when the sun rose. However, when he met Juliet, he instantly fell in love with her and Rosaline was totally wiped from his mind. He thought that Juliet was the most beautiful woman on Earth, and that he never felt true love before he met her. Romeo had changed his love so quickly when he met a girl prettier than Rosaline. What word can I describe Romeo based on these events? I was thinking some adjectives could be similar to inconstant, fake, shallow, etc. but i can;t think of the right word.
Thanks!