How does loyalty affect the outcome of Romeo and Juliet?

Romeo and Juliet are full of conflicting loyalties. The background loyalties are set up in the first scene, when Samson and Gregory decide to start a fight with some Montagues. Loyalty drags all of the surrounding Montagues and Capulets into the fray. The first loyalty that is established is loyalty to family.

But Romeo and Juliet complicate that by making obligations to each other. Now they have to be loyal, not only to their families, but to each other, and by extension to each others' families. Romeo shows this when he meets Tybalt: he refuses to fight him, because he is loyal to Juliet, and so to Tybalt. Mercutio demonstrates that there is another kind of loyalty in play here, which is loyalty to friends. As an act of loyalty to his friend, Romeo must revenge him, although this conflicts with his loyalty to Juliet's family. Juliet is caught in a similar conflict when news of Tybalt's death and Romeo's banishment is brought to her. The Nurse says, "Will you speak well of him that killed your cousin?" and Juliet replies "Shall I speak ill of him who is my husband?"