Why are benvolio and the Montagues concerned about romeo?

Romeo is a member of the Montague family, and they are concerned about him because he has been acting strangely and has been seen in the company of Rosaline, a member of the Capulet family. The Montagues and Capulets are sworn enemies, and their feud has been going on for generations. Romeo's actions are putting him in danger, and his family is worried that he will be harmed or killed.