Benvolio and Mercutio spend a fair bit of time talking to each other. You will need to specify which line you are asking about.
benvolio
Romeo's comical friend was called mercutio
In Act 3 Scene 1 Benvolio is nervous, Mercutio is careless.
Benvolio tells Mercutio to retire because he senses a brewing confrontation between Mercutio and Tybalt, and wants to avoid any violence. Benvolio is concerned for their safety and tries to diffuse the situation by suggesting they leave.
He doesn't. Mercutio is not in that scene, and Benvolio and Romeo do not part company.
Benvolio and Romeo went to the Capulets' party with Mercutio and other friends.
Benvolio serves as a foil for Mercutio because Benvolio is calm, level-headed, and seeks to avoid conflict, while Mercutio is impulsive, hot-tempered, and enjoys provoking others. This contrast highlights Mercutio's more extreme characteristics and adds depth to their relationship.
Friar Laurence
Benvolio and Tybalt was there at the scene with Romeo when Mercutio was stabbed; then died.
Benvolio, Mercutio and some other un named characters.
Although Benvolio (Romeo's cousin) and Mercutio are both loyal to Romeo, they act in different ways. Mercutio was willing to fight for Romeo; however, Benvolio was more of a pacifist and reacted to situations calmly.
Benvolio isn't more important than Mercutio. Benvolio is a good friend to Romeo (Benvolio sort of means 'well-meaning' in street-Italian), but he doesn't make much difference to the plot. Mercutio picks the fight with Tybalt that turns this from a lovestory into a tragedy. Benvolio tries to joke Romeo out of his pash on Rosaline, tries to persuade Mercutio not to fight Tybalt, tries to get the Duke not to banish Romeo - but nobody ever listens to Mercutio. A nice fellow - but not a lot of use to anybody.