Answer: Romeo is devastated because his friend, Mercutio, was killed while protecting him. Moreover, his love for Juliet made him soft and weak, unable to take action when he should have done so.
Explanation:
Romeo and Juliet is Shakespeare's famous tragedy about a two lovers and their tragic death that eventually makes their families reconcile.
In Act III, Scene I, Romeo is angry because his friend, Mercutio, lost his life to defend him. Tybalt (now a member of Romeo's family as he has recently married Juliet) challenged Romeo, but Mercutio was the one who answered it. Moreover, Romeo realizes at this point that his love for Juliet made him weak like a woman. He is desperate because his courage, once as hard as steel, has now weakened.