In the beginning of Romeo and Juliet, it states that he is in love with Rosaline. A little later, the Capulets are having a feast. Romeo thinks it would be a good idea to go, just to see his dear Rosaline. And because he was a Montague, he and his friends wore masks to conceal their identity. At the party, Romeo caught a glimpse of Juliet, where he automatically fell in love with her, therefore forgetting Rosaline.
But his original reasoning for attending the ball was to see Rosaline, who he thought was his true love. We know this because a servant of Capulet's asks Romeo to read the guestlist to him. since the servant is illiterate. This Romeo does and reads that one of the guests will be Rosaline. Benvolio then says, " At this same ancient feast of Capulet's sups the fair Rosaline whom thou so loves with all the admired beauties of Verona. Go thither and with unattainted eye, compare her face to some that I can show, and I will make thy swan look like a crow." Romeo replies, "I'll go along, no such sight to be shown, but to rejoice in splendor of my own." In other words, Benvolio wants Romeo to look at other girls, who will take his mind off of the unattainable Rosaline, but Romeo says he will go, not to look at the other girls, but to enjoy the sight of Rosaline.
Romeo wanted to get a chance to see Rosaline again.
Rosaline was on the guestlist. If she hadn't been, Romeo wouldn't have bothered showing up. Rosaline was invited because she is a Capulet, Juliet's cousin.
Romeo and his friends Mercurito and Benovlio gatecrash the party because Romeo's beloved Rosaline was going to be there
Romeo is lovesick for Rosaline, who has vowed to remain chaste. Romeo's cousin Benvolio suggests that they sneak into the Capulet's feast so that Romeo can get his mind off of Rosaline. When Romeo and Benvolio crashed the party Romeo met Juliet and they fell madly in love with each other. The place they meet is at a feast in Capulet's house.
Rosaline is one of the guests, and she's the girl he's got a crush on.
Rosaline is the girl that Romeo loved before he met Juliet. She is only in the beginning of the play and she is only mentioned; she doesn't actually say anything. Romeo chooses to go to the Capulet's party because he thinks he will see Rosaline there. Except Rosaline doesn't love Romeo back
Romeo considers crashing the party when he finds out that Rosaline will be there.
Romeo should attend the Capulet party because it presents an opportunity for him to see Rosaline, the woman he is infatuated with. Additionally, attending the party allows him to socialize, have fun, and potentially distract himself from his unrequited love for Rosaline.
Benvolio and Romeo went to the Capulets' party with Mercutio and other friends.
Benvolio was planning to go to check out the girls. He talks Romeo into coming because Rosaline, the girl who refuses to listen to Romeo's protestations of love, will be there, partying it up. Romeo's intention is to hang around Rosaline, but Benvolio is hoping that some other girl who is at the party will make Romeo forget about her. This is a plan which is more successful that Benvolio can imagine.
Scene 2: Juliet's father wants her to get to know Parisbefore she marries him. A servant of the Capulets has a list of names to go to a party. He can't read so he asks Romeo to read it and he sees Rosaline's name on it. Benvolio wants Romeo to go so he can maybe forget about Rosaline.
Unfortunately that is a question that has no answer. Rosaline's role in the story of Romeo & Juliet was only meant to serve as a plot device for the telling of the story. Without having first loved Rosaline, Romeo would have never known what it was to fall in love with Juliet. It was simply through Rosaline that Romeo was able to get gain entrance into the Capulet's party, so that he could then catch a glimpse of Juliet in which he would fall in love with her. For instance, before Romeo knew Juliet, he hated the Capulets, as he was a Montague. It was the relationship he had with Rosaline that, and this is speculated through interpretation, caused Romeo to be able to view the Capulets through different eyes and begin to see with his heart, thus he didn't hate Juliet, and fell in love with her...in a love that was more mature than that which he had for Rosaline. Perhaps and earlier draft of Shakespeare's play might have set up the relationship between Romeo and Rosaline more thoroughly, in how they met.