You're gonna cry :)

Spoilers about the third part!!













Part 3 (raws)_ https://myreadingmanga.info/nine-dot-double-suicide-iii-kuroko-no-basuke-dj-cn/

Most important pages for this Theory _ http://www.mangago.zone/home/album/170991/

So, it's from a comment thus is not confimed, BUT it makes a LOT of sense.
In the non translated third part we're exposed to a very interesting last painel.
In the last pages we can see aomine's sister going into his place and finding a concerning amont of trash and being susprised/confused about something.
At the first chapter we can see Aomine getting ready for something (like a party) and as we all know Kagami is getting married.
And in the first painel of the series we see a pair of fine shoes hanging.
So the theory goes like this: at the first chapter we see Aomine getting ready to go to Kagami's marriage. But, Aomine, consumed by sadness (maybe after seeing the box again?), does not make it to the party, and commits suicide right on the spot, with the clothes he was going to wear.
If that's actually the case, there'll most likely never be a part 4 ;-;

Ps: reading a bit more into it, Aomine commits suicide while Kagami is still alive. So why DOUBLE suicide? Well, that's because with the marriage Kagami is killing himself in a emocional level, burying the feelings he has for Aomine, thus the title.