What did Romeo learn from his experiences?

The answer to this question regarding William Shakespeare's drama Romeo and Juliet depends entirely on when in the play you ask this question. What I can do is break down the play by its acts and scenes and indicate spaces in which Romeo could have learned a lesson: 

I.i: Romeo learns that love can easily lead to heartbreak

I.ii: Romeo learns that Rosaline will be in attendance at the Capulets' party

I.iv: Romeo learns that...

The answer to this question regarding William Shakespeare's drama Romeo and Juliet depends entirely on when in the play you ask this question. What I can do is break down the play by its acts and scenes and indicate spaces in which Romeo could have learned a lesson: 

I.i: Romeo learns that love can easily lead to heartbreak

I.ii: Romeo learns that Rosaline will be in attendance at the Capulets' party

I.iv: Romeo learns that his friends are tiring of his heartbreak, and care about his well-being, as demonstrated by Mercutio and Benvolio's efforts to cheer him.

I.v: Romeo meets Juliet and learns what "love at first sight" is

II.i: Romeo learns that Juliet loves him as well and is willing to be with him despite their families' conflict

II.iii: Romeo learns from the Nurse that Juliet does plan to escape, meet, and marry Romeo

II.v: Romeo learns how much Juliet loves him, and is counseled in patience and caution by the Friar

III.iii: Romeo learns that he has been banished and that, despite his crimes, Juliet still loves him. 

V.i: Romeo learns of Juliet's "death"

Hope this helps!