Does Benvolio tell the truth in his account of fighting act 3 scene 1?

Yes, based on the evidence in that scene, Benvolio's account of the fighting is accurate. While he may be biased towards his friends and family, his overall description of the events leading up to and including the fight between Tybalt and Mercutio seems truthful and consistent with the actions and dialogue of the other characters involved. Benvolio states that Tybalt, enraged by the Montagues' presence at the Capulet ball, provoked Mercutio with "bitter words." This leads to a verbal confrontation, with Mercutio responding to Tybalt's insults and challenging him to a duel. Benvolio confirms that he tried to intervene and prevent the conflict but was unsuccessful. Tybalt then draws his sword, and the fight begins. Benvolio's account is supported by the actions and dialogue of Mercutio and Tybalt throughout the scene, as well as by the reactions of the other characters, including Romeo and Paris.