I think porphyria was killed because her lover didn’t Realy like her or think she was beautiful and because everything was happening so fast he panict and decided the bet way to get out of his situation Was to murder her. I think this because of where he says “A sudden thought of one so pale for lover of her, and all in vain: so, she was  come through wind and rain”. As I said before this suggest that she was unattractive and was very forceful towards her lover. He uses the word pale as an adjective to describe her presents .