What has the reader learned from Shakespeare's Romeo and Juliet?I am unsure of what to write about....maybe we learn that we should not love a...

Let us examine your statement:  "Maybe we learn that we should not love a person so much so that the relationship can last longer?"  This statement underscores precisely the theme of one of Friar Laurence's didactic speeches.  In Act II, Friar Laurence instructs Romeo,

These violent delights have violent ends,

And in their triumph die, like fire and powder

Which as they kiss consume.  The sweetest honey

Is loathsome in his own deliciousness

And in the taste confounds the appetite.

Therefore, love moderately, long love doth so,

Too swift arrives, as tardy as too slow. (9-15)

Clearly, your statement touches upon the response in the previous post; that is--to use academic language--the theme of impetuosity.  For, this theme is prevalent throughout the play as almost every character exhibits irrational haste, even the Friar himself as, in fear, he runs from Juliet's tomb leaving her alone.  So, stay with your original idea and develop it, since often our initial reactions to a literary work are intuitively accurate.

As you look for support, consider the hasty actions of Lords Montague and Capulet as in cholera, they wish to duel in the streets of Verona even though they know that such actions are against the law.  Likewise, Mercutio and Tybalt engage in heated words and impetuous actions, along with Romeo, who hastily intervenes--albeit meaning well--and causes Mercutio to be gravely injured. 

Most impetuous of all, Romeo wishes to marry Juliet immediately because their erotic love is a "violent delight" that they wish to satisfy.  The tragic end to their love is due to this haste.  Indeed, how often the satisfaction of one's erotic feelings prevents the development of a lasting relationship in real life. Studies have shown that if couples will really get to know each other over time, they will develop a more meaningful and lasting relationship, one which can withstand conflicts and difficulties.  (For support, you may wish to do some research on this last idea as magazines have featured such articles.) At any rate, time and time again throughout the play, poor choices because of haste are more the cause of the tragedy than the cursed fate.