Tone in "Porphyria's Lover"

This poem starts out with the first two lines describing a calm evening, but soon in line 3, it starts to gain some momentum when it says, "It tore the elm-tops down for spite," this referring to the strength of the wind. The tone changes again from being stormy outside to being calm inside when Porphyria enters in line 7. In line 9, the speaker tells the reader, "...all the cottage warm." The tone given in lines 7-9 gives the reader a cozy and comfortable feeling even though in line 11 it is said that she had a "dripping cloak and shawl." In line 15 when Porphyria calls his name and there is no reply, she simply "puts his arm about her waist" in line 16. This could have easily been an intense moment, but nonetheless, the reader still has that cozy feeling inside. The next several lines (17-34) still contain that cozy feeling while she tells her lover that she does indeed love him and he realizes that she "worships him." This is when the tone makes a turning point in the poem. He is debating what to do, and finally he decides to "strangle her with her own hair" in line 41. He doesn't seem to think she felt any pain and seems to be simply happy that Porphyria's wish came true (line 57). From lines 58 to the end, he is happy that she died with him and that he can have her love forever more!