Theme of Porphyria's Lover

The theme of "Porphyria's Lover" by Robert Browning is one that I was able to pick out. The main character has the girl of his dreams come to him and be close to him. He even says she is "Murmuring how she loved me"(Browning l.21) and he assumes that her one wish is to be with him forever. Unfortunately he doesn't realize that she would willingly be with him forever and takes it into his own hands to make sure that she is by killing her and keeping her dead body close to him but he believes that he is merely granting "Her darling one wish would be heard."(Browing l.57) The man in this poem is clearly delusional but the theme to me is that he believes she will not willingly stay there and her one wish is to somehow still be with him forever.