September

[RiverNotch]

The season finally slumps "Slumps" is a silly word: makes me think either of the death of someone sitting down, or a quaint way of referring to a failure. This could probably be a nobler image, too -- something about leaves falling, about a warm brass beginning perhaps to round off the warm brass end.
and in the tender light behind the pane, 
tired glances upon swirling glasses; I disagree with the semicolon. This for me generally indicates separation of thought much less effectively than the long, spatially distancing em dash. Also, I'm not entirely sure what you're trying to convey with this line, especially with "upon" -- tying to the next line, I imagine couples discussing matters over tumblers of bourbon, but then that should be "over", not upon. Unless you are talking of something very tired about the way these couples treat their drinks -- but then, that would be a bit off, I think.
couples pretend worlds I like this line, though I'm somehow thinking that the couples imagine themselves to be those worlds -- slightly off, but for me very, very appropriate.
from their worn leather couches, 
and fade away on a warm brass note. It's the "warm brass note" that makes me think more of alcohol than of autumn, though both are not mutually exclusive -- music here is a secondary thing, what with the lack of music all throughout (light, perhaps, but what light? If orange, would be redundant -- this could be a liability. If your goal is something other than plain orange light, you'll need to tweak the poem by bits, though how is up to you -- if your goal is to present simply that light, or this plain season, you might be thinking too one-dimensionally, at least for something this long). The whole feel of sweet, swirling loss in this poem is a real treat, though it's not as seasonal as I would like -- again, that first line could probably be changed. And I'm good with the line breaks -- the longer, dreamier lines fit the subject better.