Proof that Romeo and Juliet is a tragic love story include that Romeo killed himself due to a misunderstanding because he believed Juliet was dead, and then she killed herself out of grief.
Divisions of proof are explanations of why your thesis statement is true. For example, you need to establish elements of tragedy. One element is that Romeo and Juliet fell in love, but they did not know the family each belonged to. They fell in love under the naïve premise that all you need is love, and family connections are not important. Of course, the reality of their situation came crashing down on them.
Is she a Capulet?(125)
O dear account! my life is my foe's debt. (Act 1, Scene 5)
It is tragic because they already fell in love, at first sight, and they do not know what is in store for them.
A second division of proof would have to address the fact that they actually are in love. You can do this by establishing that it was not just a one night enchantment. The next day, they were still in love.
Bid her devise some means to come to shrift
And there she shall at Friar Laurence’ cell
Be shriv'd and married. (Act 2, Scene 4)
Unfortunately, the two young lovers only get one night together, which demonstrates the tragedy: Romeo kills Juliet’s cousin Tybalt in a brawl and is banished. They are still deeply in love, and have to part.
Finally, the tragedy should be not of their own doing. To be really tragic, the characters can’t really bring it on themselves through misdeed. Yes, they were foolish. Yet they didn’t do anything immoral. Their deaths were the result of their parents callousness and miscommunications, such as the fact that Friar John was not able to deliver the letting telling Romeo what was going on.