I like it a lot, Matt, though it seems more like a “Plaint” than an “Epistle,” since there’s no discernible addressee. Is that the point: loneliness writing to no one?
I enjoy how this opens with straightforward metaphor and statement and segues into non sequitur.
The horse flesh after the cherry blossoms (I had to look up sakura) would go down easier, pardon the pun, if there were a period after “liking.” That would signal the more abrupt shift.
The settling of the various images at the bottom or end is a lovely and poignant summing up of the poem’s contrasts.
A couple things:
I’d like commas before and after “come morning” in L2.
I agree with Sarah-Jane about “gung-ho” in S4L1. Do you need an adverb there. Maybe, but I also wonder if “launch itself” could be improved upon. I don’t have an alternative in mind, but that verb for me suggests a more rocket-like motion, whereas the blossoms fall and are blown about. I think what you’re getting at is unselfconscious risk-taking or self-surrender, but launching and especially gung-ho launching sounds more aggressive or perhaps guarded.