O, I am a Fortune's fool!

In Act 3 scene 1 Romeo kills Tybalt, Juliet's cousin, after he has married Juliet. Directly after killing him he says, "O, I am a Fortune's fool!" In the guide to shakespeare, the word "O" declares an exclamation of emotion. One can read this in many different ways. Emotion can be used in a melancholy sense, an agitated, pain, or in many other ways. Here, I believe Romeo is using "O" to exert his frustration of his stupidity. He is perfectly aware of the new rules laid out because he says them a few lines earlier when he tries to break up the fight. In this sentence, Shakespeare capitalizes the word fortune to make it Fortune. This could mean he is using personification and making the word fortune into an actual person like figure. Fortune in this sense is his future. He says he is a "Fortune's fool," which means that he is foreshadowing that he knew that marrying Juliet would result in something unfortunate, and now it has happened. The book claims that "fool" means a plaything. This statement is a product of his life being played with by a puppet like figure (Fortune) which ends up being his true love. His true love for Juliet is so strong that he will do anything and kill anything so that he can defend it, when in reality, he ends up hampering the ability of the relationship to work because he is now ostracized from the community.