He would stay in his room, without leaving it, and he would always cry, and he wouldn't try to find comfort in anything else. He would also wish for death, because apparently there was no point in living without Rosaline.
The previous answer is an accurate response, along with what he felt for Rosaline affecting him emotionally remember that in Romeo and Juliet, it is stated, Rosaline does not, in fact, love Romeo back at all. This leads Romeo to go to the party in Act I, Scene I and well, the rest is history.
