I feel really sorry for Rosie. Basically she's had done to her what was done to Kendall. She over invested too quickly, and she's clearly devastated he did it to her too. Kendall handled it with much more dignity,
I think we have to remember these people have been together for a week or so, they don't know each other, and people like Adam are very young at 22 years old.
In real life at this age, if you've been with someone for a few days, a handful of dates and they decide they prefer someone else, you just move on. You don't go full on bunny boiler "it was real" crap. I don't think Rosie handled it well. She was too invested too quickly.
And I've no clue what Laura is doing, at 29 I'd expect her not to be losing her shit over a twenty year old she's known two weeks.