In my opinion the theme of "The Bells" is the story of a tragic loss. The theme about changing seasons made sense as well, but the story of a tragic loss has more textual evidence rather than inferences. In the first stanza the author was talking about joyous silver bells, and it makes it seem as the stanza is about love at first sight. For example, "What a world of merriment their melody foretells!" (Poe, Stanza 1, Line 3, The Bells), this is showing that Poe, at the time, was very joyful. As we go into stanza two Poe makes it as if he was getting happily married with the love of his life. As it states, "Hear the mellow wedding bells—" (Poe, Stanza 2, Line 15, The Bells), it says directly in the text that the golden bells were wedding bells,
