In Shakespeare's Romeo and Juliet, I think there is a distinct difference between a tragic flaw and making mistakes.
The concept of the tragic flaw is attributed to Aristotle in his Greek tragedies. It comes from Aristotle's characteristics of a "tragic hero." Shakespeare's tragic heroes are in plays such as Hamlet, Macbeth, Othello (heroes and plays have same name), and Brutus in Julius Caesar (to name a few).
First, the tragic hero must be a great man—this does not mean having a good sense of humor or being who is entertaining at parties. "Great" in this context means "celebrated," "brave," or "respected"—men who have, for example, proven themselves in battle, e.g., Othello or Macbeth. The tragic hero must have a "tragic flaw."
...the hero's misfortune must be brought about 'by vice and depravity but by some error of judgment.'
Othello is overly jealous. Macbeth states that his biggest problem is his "vaulting ambition:" he wants to have more than he has and be more important than he already is. Second, he must die. Finally, the tragic flaw must be responsible for the hero's death.
I don't see Romeo as a tragic hero. He is not a great man. He is a young man who spends most of his time early on in the play piteously moaning over a woman who is not interested in him. He is not very mature. It is hard to take Romeo seriously, especially in that he really does not do anything heroic. He is not a soldier, and he is not the leader of his noble family. If anything, Romeo is just too young.
After he meets Juliet, it can be argued that he turns himself around: he finally seems to understand what love really is. However, "seems" is the operative word. Had Rosalind loved Romeo in return, can we be sure he would not have loved and revered her in return? Is there any way to know that Romeo only seems to come to his senses because he meets a beautiful woman who returns his "love?" We cannot always choose who we fall in love with, so I can't say that he is foolish for falling for Juliet (in that his family hates hers).
However, when Romeo first believes he may not be able to be with Juliet, the first thing he threatens is suicide. He does not keep his head; he does not look rationally at the situation (as does Friar Lawrence) to see if there is some means by which the problem could be solved.
As if that name,
Shot from the deadly level of a gun,
Did murder her; as that name's cursed hand
Murdered her kinsman. O, tell me, friar, tell me,(110)
In what vile part of this anatomy
Doth my name lodge? Tell me, that I may sack
The hateful mansion.
Draws his dagger.
Hold thy desperate hand.
Art thou a man? Thy form cries out thou art;(115)
Thy tears are womanish, thy wild acts denote
The unreasonable fury of a beast.
Unseemly woman in a seeming man!
Or ill-beseeming beast in seeming both!
Thou hast amaz'd me. By my holy order,(120)
I thought thy disposition better temper'd.
Hast thou slain Tybalt? Wilt thou slay thyself?
And slay thy lady that in thy life lives,
By doing damned hate upon thyself? (III.iii.107-125)
Romeo is ready to take his life because he is banished from Verona. Foolishly, he never considers another plan; he does not stop to think of how the news is affecting the woman he swears he loves so much; and, foolishly he does not consider how killing himself will affect Juliet.
For me, I find that Romeo is simply too young. That is his flaw. He is not a hero, so I cannot find a "tragic" flaw.