The only good result of love in this play is that Romeo and Juliet are briefly happy when they are in love (before all the dying), and the feud ends after they die.
There are pretty much no happy relationships in Romeo and Juliet. Shakespeare seems to want us to believe that love has tragic consequences.
Romeo is pining for his ex-girlfriend Rosaline when the play begins. It seems that Rosaline has decided to remain chaste. Poor Romeo is miserable.
Griefs of mine own lie heavy in my breast,
Which thou wilt propagate, to have it prest
With more of thine. (Act 1, Scene 1, p. 15)
When Romeo meets Juliet, we think things are looking up. Unfortunately, they are not able to escape the curse of the family feud. Romeo fights with Tybalt and is banished. He secretly marries Juliet, and they have one night together before he has to leave town. Romeo says he would rather die than leave.
Let me be ta'en, let me be put to death.
I am content, so thou wilt have it so. (Act 3, Scene 5, p. 78)
Of course, Romeo does leave. Juliet’s parents have no idea about Romeo. They decide it is high time Juliet got married, since she is no spring chicken at fourteen. They have a great match for her in Paris, a nobleman and friend of her father’s. The fact that Juliet does not want to marry him matters not. Her father tells her to either marry Paris or get out of the house for good. Juliet agrees.
Juliet can’t marry Paris, of course, because he is already married to Romeo. She goes to Friar Lawrence, Romeo’s mentor, for help. He tells her he can give her a special potion and she will seem dead, then Romeo will come get her. It sounds good to her—anything is worse than marrying Paris. She agrees.
Shakespeare has us believing that love will win. Unfortunately, his message that nothing good can come of love is carried out. First, Romeo’s mother dies from the stress and grief of her son being banished.
Next, Romeo kills himself because he thinks Juliet is dead.
O my love! my wife!
Death, that hath suck'd the honey of thy breath,
Hath had no power yet upon thy beauty. (Act 5, Scene 3, p. 108)
She wakes up and tries to kill herself with the poison he took, and when there’s none left she stabs herself. Shakespeare warns us of this in the prologue.
A pair of star-cross'd lovers take their life;
Whose misadventur'd piteous overthrows
Doth, with their death, bury their parents’ strife (p. 8)
The only good to come from the whole thing is that it seems the feud is over. Romeo’s father and Juliet’s parents feel so bad they decide to end the feud. Something good did come from love in the end.