Hey, Romeo is a "loverboy". He is an adolescent that falls hard and fast in "love”. There is no middle ground with this guy. He sees life in absolutes. With Juliet he is absolutely happy and without her he can kill himself. There is in him a sense of loyalty to his mates, Mercutio in particular. Mercutio's death brings about temporary rage which again represents absolutes within his personality.
Mercutio is loves Romeo. We can make a good argument that his love for Romeo is sexual in nature as much as it is brotherhood. His frustration comes out in his famous "queen Mab" speech. Mercutio covers much of his emotions with jokes and violence.