Well to breathe life into the idea once again...the cherry blossoms blooming signify something grim in this oneshot, and I would not call it farfetched to label them as deathly. And this author was very diligent with shading the entire time, so to think that her coat not being shaded was purely an accident is unlikely. I would say we have sufficient evidence to say she was having a painful and nostalgic recollection of that day a couple years later...regarding her unrequited love partner, though?
I will point back toward the cherry blossom tree once again. The trees seem ravenous and parasitic...feeding off of dead dreams. Now from what I've gathered there are two possibilities: either it's feeding off of Re's dead dreams or it's feeding off of Fuyu's dead dreams. This leads into either the route where the trees are sapping off of their dead high school dreams and that be it, but! that would make the timeskip portion seem pointless and weak. It doesn't gel together too well. There are a few possible other routes, but the only one that encompasses the pinnacle of both their dreams dying is Fuyu committing suicide. Not only is Fuyu's dream of being a ballerina dead, but Re's dream of Fuyu officially 'dies' completely along with her.
I don't particularly think that this has to be the case though. It very well could be simply Re painfully and wistfully recalling that day (which probably hurt her a lot) when she steps into the train station again. This also carries a lot of weight, and is a sufficient explanation for the imagery used.
So, in conclusion, I think it is impossible to rule suicide out as an option, but it is equally impossible to declare it the perpetrator.
...man I love non-Western storytelling. So much dissection you just can't do in any other genre.