Once: they meet for the first time and fall for each other immediately after.
He imagined himself to be in love with Rosaline, but Juliet was the real thing.
Romeo. Hence the name "Romeo and Juliet"
The Capulets throw a big feast in Romeo and Juliet where Romeo and Juliet first meet and fall in love.
They fall in love at first sight
Romeo and Juliet. Mercutio: Didst thou not fall out with a tailor for wearing his new doublet before Easter? (Act II Scene 1)
No, Juliet is not single.
Romeo isn't destined to marry anyone. He does fall in love with Juliet. Juliet is the one that is destined to marry Paris.
Juliet
It was love at first sight :]
Romeo and Juliet meet, fall in love, and get married.
Early in the play, Romeo and Juliet meet at the Capulet's party and they both fall in love at first sight.
Romeo is Juliet's lover. He is, as is obvious, one of the two main characters of the story. The basic storyline goes that Romeo and Juliet's families are enemies, but Romeo and Juliet fall in love, get married secretly, then Romeo gets exiled because he killed Juliet's cousin, then Juliet wants to be with him so she fakes her death, but Romeo doesn't get told it's fake and rushes back to where they live, and they both die.