"Without the fuel from Peragus, Citadel Station cannot maintain its orbit. It will crash into the planet, and its destruction will echo across twenty other worlds."

 

During the Battle of Telos I guess. Although I'm not quite sure why it gets destroyed, since you do stop the attack, and you do set up trade between Telos and Sleheyron

It is probably from the scrapped stuff where you join Nihilus...

Come to think of it, you only get to choose between Czerka and the Ithorians, there's no way to actually screw the galaxy in this game. I found this too

 

"The skies of Telos shall be shrouded in ash for a century, all that the Republic wrought there serving only as ruins to be uncovered by historians. These worlds, like Malachor and Korriban, will become home to darkness, creating new evils that will rise to threaten the galaxy."