Should work in the Newgrounds Player, but otherwise you can find it on Kongregate where it runs using ruffle.js :) Not sure I'm that proud of this old fan game any longer though :D https://www.kongregate.com/games/peterinns/sonic-abstracta

I've rewritten these characters more times than I'd like to count, but from what I could dig up from this time, the event that triggered their falling out was Ashes joining GUN, and the resulting paths they took afterwards put them further at odds with one another.