How are sex and death related in Romeo and Juliet?

When you consider that Romeo and Juliet fall for one
another - largely due to a sexual (or physical) attraction, and then that the long
standing fued between their families has been resulting in hatred and violence for many
many years, you could conclude with this statement: Because what started as a physical
attraction lead to marriage, Romeo and Juliet were destined to
die.

Think about the order of events in the story.  Romeo
goes to the Capulet party (knowing fully that he is not invited) to get over his
attraction to Rosaline.  He falls immediately for the beautiful Juliet.  They rush into
a very immature relationship.  They get married quickly in part, because in those days,
sex was out of the question before marriage.  On the very day Romeo is excited to spend
his first night with his new wife - his genuinely pleasant attitude angers his now
cousin-in-law, Tybalt, provoking him to a fight.  Mercutio dies.  Tybalt dies.  Romeo is
banished (a fate just as bad as death).  And through a series of slightly more
complicated events, both Juliet and Romeo die - all because of Romeo and Juliet's
physical desire for one another.

If the two had waited to
cultivate a more mature love for one another - one that went beyond just the physical
attraction (one that undoubtedly takes more time), we can assume a few things would have
happened differently.  Certainly they would have been more level-headed in decision
making.  Likely they would have eventually included their parents/families in the
relationship, rather than keeping it a secret.  Hopefully this would have brought the
two families together before a hasty wedding, and therefore
prevented the violence and death.

I think a major lesson to
be learned here (that isn't so far from reality) is that "new love" based very highly on
a physical attraction can lead to hasty and immature decision making - which can be very
destructive.