Two families, the Montague's and the Capulet's have a violent feud that causes them to endanger civilian lives during their duels.
Two households, both alike in dignity... from ancient grudge break to new mutiny/ where civil blood makes civil hands unclean. (1.1.183)
Romeo pines for Rosaline, his unrequited true love.
She will not stay the siege of loving terms/ nor bide the encounter of assailing eyes...She hath forsworn to love, and in that vow/Do I live dead that live to tell it now. (1.1.191)
Romeo and a few others decide to go to the Capulet ball (Where they, Montagues, are not welcome) in hopes of curing Romeo's heartbreak, but Romeo sees someone that will change his life forever, Juliet Capulet.
O,she doth teach the torches to burn bright!/ It seems she hangs upon the cheek of night/ Like a rich jewel in an Ethiop's ear-/Beauty too rich for use, for earth too dear!/ So shows a snowy dove trooping with crows. (1.5.201)
As Romeo leaves the party he climbs the garden wall and sees Juliet at her window.
O Romeo, Romeo! Wherefore art thou Romeo? (2.2.210)
What light from yonder window breaks? (2.2.209)
They decided to get married and a few days later they were husband and wife.
On the same day Juliet's cousin, Tybalt, killed Romeo's friend, Mercutio, in a duel and Romeo seeks vengeance, killing Tybalt in the process.
... Mercutio's soul/ is but a little way above our heads,/ staying for thine to keep him company./ Either thou or I, or both, must go with him. (3.1.232)
... If the measure of thy joy/ be heaped like mine, and that thy skill be more/This neighbor air, and let rich music's tongue/ Unfold the imagined happiness that both/ Receive in either by this dear encounter. (2.6.226)