In researching for a short story I'm writing, I remembered a poem I read in high school literature class, in which the author kills his lover to freeze the perfect moment with her, so that it would never end, never change, her love for him would never fade. I thought it was Poe, but looking for it I did come across "Porphyria's Lover" by Robert Browning which might be what I was looking for. Just in case, if anyone is reminded of other works, I'd love to find more stories or poems with similar themes. Thanks!