Ask for me tomorrow, and you will find me a dead man

means if you try to find him tomorrow  he will be in his grave

a plague on both your houses

means there houses are as bad as eachother

they have made worms’ meat of me

means his body will be eaten by the worms

O sweet Juliet, Thy beauty hath made me effeminate, And in my temper softened valours steel!

it means that Juliet made him soft