Benvolio suggests that Romeo forget about Rosaline and look for romance with someone else. Romeo, however, rejects the advice initially but ultimately ends up romantically linked to Juliet rather than Rosaline.
Romeo's love for Rosaline and rejection of Benvolio's advice is an allusion to the sonnets of Petrarch. Petrarch wrote of men who wildly loved women who rejected them and would accept no counsel from anyone. Shakespeare often parodied Petrarch, both in this character trait of Romeo's and in Shakespeare's own sonnets. Shakespeare's Sonnet 130 is the most biting parody of Petrarch.
As the play progresses, Romeo realizes that his love for Rosaline was false and his real love is for Juliet. In turn, this is Shakespeare suggesting that Petrarch's model of love is false.