Both of these poems are what are known as a dramatic monologue as well as being written in the first person. The duke and the lover disregard the women's feelings and physical well being in favor of their own selfish love.
In both stories, the lover's perceive the women as objects, instead of actual people. Romeo and Juliet is about two lovers - who adore each other so much, similarily Porphyria's lover is about a man who loves Porphria so much, which leads on to him killing her.
He lives in a cottage, somewhat distant from the main house. It is evident that this man has a sadistic personality, accompanied by a twisted sense of perception that is fueled by a gnawing insecurity within his own personality.
It is apparent that the speaker works for Porphyria's family. Robert Browning gave this to them through his poems. Dramatic monologue can also be known as a persona poem.