Romeo and Juliet is a tragic love story because two young people fall in love, but their love is forbidden and it results in both their deaths.
The above could be an example of a one-sentence summary, because it does summarize the tragic love story element. Right in the prologue, Shakespeare tells us that this is going to be a tragic love story.
From forth the fatal loins of these two foes(5)
A pair of star-cross'd lovers take their life;
Whose misadventur'd piteous overthrows
Doth, with their death, bury their parents’ strife. (Prologue)
The two are described as “star-crossed” because they were destined to be in love. Unfortunately, the families were feuding. As a result, they almost didn’t meet. It was not until Romeo’s girlfriend dumped him and his friends forced him to go to the Capulet ball.
The tragic part is that Romeo killed Tybalt in a duel, in self-defense and defese of his friend Mercutio. Romeo was banished, and married Juliet in secret. But then her parents wanted to force her to marry, so she had to fake her death. Romeo found her and thought she wa dead, and the next thing you know he kills himself and then she wakes and kills herself.
There are different versions of one sentence summaries you can use, such as: Somebody Wanted But So Then.
Romeo and Juliet wanted to get married but their families were feuding so they married in secret and were separated then each one ended up committing suicide thinking the other was dead.
Now you try!