For one thing, while Romeo does seem fickle at first, Rosaline has a purpose. She's meant to show us how Romeo changes over the course of the play. In the beginning, he was basically in the throes of puppy love--going on about her looks, her smile, blah, blah, blah. There were no hurdles beyond her own disinterest, no real love. It was shallow, and meant to be seen as such. Once Juliet comes into the picture, though, Romeo starts to grow up. He starts thinking about more than looks, starts weighing consequences, and by the end, he's willing to choose death over a life without Juliet (which is still stupid to me, but he wouldn't have even considered that for Rosaline). Rosaline was never more than a foil.
And though their relationship came on quickly, I think that was mostly due to the time constraints. Shakespeare had to have them meet, fall in love, and off themselves within a very short period. There wasn't time for frequent meetings or any of that. It had to happen quickly...and though I'm the last person to believe in love at first sight, they (and the people who would watch the play being performed) often did. Courtly love, romantic love...that was the ideal for the time period, even if it wasn't ever the reality. Of course Shakespeare included it--he had to appease the higher classes.
Besides, marriage wasn't something that took a lot of thought on their part. They were financially and socially matched, and it wasn't as though they were wondering whether or not they could handle living together. That's something people in our time, not theirs, think about. They were probably just glad to have found someone on their own as opposed to an arranged marriage with a stranger. It was enough for them.
Romeo wasn't supposed to be a stalker. He was supposed to be a romantic...though I do agree with you. He annoys me. A lot.
There WAS love, though. Selfish love at times. Immature love, but still love.
This was actually one of Shakespeare's more brilliant plays. I may pretty much hate it, but I've studied this one in depth. The things he does with the language is just brilliant, even if it does take a LOT of study to appreciate it. He put a lot into that one.
