Romeo is fickle in many way's.
1) In the beginning we see him as an innocent character that hated the mere thought of fighting and violence, but that soon changed after Mercucio's death. His thirst for revenge brought him to the stage of murder, You could also say that the violence through the feud had got to him.
2) His 'love' for Juliet? Was it in fact love? Was it not just mere infatuation, and was he not just 'lusting' for her. The balcony scene tells us that he just wanted to sleep with her, and Juliet would only let him have his way if they got married.
As you can see Romeo is not a perfect character as many have suggested, but instead an imperfect and fickle character indeed.
-Kerry Ingram :]