He did not know that Romeo and Juliet were married, and neither did Tybalt. But it didn’t make the problem any better by stirring a fight with him. The fighting started when Tybalt asked to talk to them, and Mercutio replied with “ And but one word with one of us? Couple it with something; make it a word and a blow.” This is literally just asking Tybalt to fight with him. The last way Mercutio was at fault for Romeo and Juliet's untimely demise is getting himself killed in the fight with Tybalt.He is angry that he is wounded, because he clearly states “ I am hurt. A plague on both your houses! i am sped. is he gone and hath nothing?”( act 3 ac1 pg 231). He shows that he is upset at Romeo for getting in the way of the fight by wishing a plague on his house. And this is what makes Romeo want revenge.
If he hadn’t of gotten himself killed, Romeo would not have gone after Tybalt and killed him in a mad rage, hoping for revenge on Mercutio. The hope for revenge is what got him banished. Also, If he hadn’t have gotten banished, him and Juliet would’ve been able to run away together without the worry of death. But instead, Romeo was only thinking about revenge at the time. The moment he decided he wanted revenge, was when he heard that Mercutio was dead. “ This days black fate on mo days doth depent; this but begins the woe others must end.” (act3 sc1 pg231) This was his split