"What happened to Rosaline who you were in love with a few hours ago?"
Since nobody knows about them, nobody threatens them. Or perhaps you are talking about Tybalt's desire to fight Romeo and the challenge he has sent him. It is hard to answer without knowing what "threats" you mean.
He means that they react to what they see when they see a beautiful woman without internalizing any feelings. Their reaction is totally superficial and governed by hormones. That would certainly be an accurate assessment of someone like Mercutio, or of Romeo when he was after Rosaline.
Juliet tells her father that she has "learned...to repent the sin Of disobedient opposition" and she begs his forgiveness. She's lying, of course, because she has the potion form Friar Lawrence to help her plan her escape. Capulet is so excited by her apology that he decides the wedding should be moved up to Wednesday.
Romeo should find out by Friar Jon bringing him a message from Friar Lawrence. The message also would include how she is not really dead. A better way for you to find out would be to READ Romeo and Juliet. Seriously it's not that bad of a book.
Romeo and Juliet have a number of conversations in which Romeo can react to many things Juliet says. In other words, this cannot be answered unless it is more specific.
Romeo does not like the fact that he is being banished, describing that it is worse than death itself, because of the fact that he will have to live without being able to see the love of his life, Juliet. He throws a temper tantrum, explaining that a fly is more free than he, and that fly will be able to see Juliet, but Romeo will not. Friar Lawrence tells Romeo to man up, and to be thankful for the fact that Romeo is not going to be put on death's row. Again, Romeo explains how death would be better than banishment.
They are heartbroken.
Juliet reacts with shock and horror when she is told she is marrying Paris, as she is already married to Romeo. She refuses to comply with her parents' wishes and seeks the help of Friar Lawrence for a solution.
They are very shocked and sad, of course.
No records exist of contemporary performances of Romeo and Juliet.
Romeo is more optimistic about it. Juliet is much sadder and is very upset that she won't see him anymore where as Romeo knows that he will find a way to see her again. Romeo thinks that banishment is a harsher sentence than death, according to what he says to Friar Lawrence when Lawrence tells him the verdict.
She tells her everything about her love being Romeo.