There is one thing Iíve been wondering about this theory of yours Jediphile. If Darth Nihilus was a dark manifestation of the Exile (or in other words, the dark side the Exile rejected at Malachor V), how come you can fall to the dark side in TSL? Shouldnít it be impossible for the Exile to do, since that dark side of his/her self isnít in him/her? Or is this just a massive misconstrue on my part?
It is merely the Dark Side that the Exile rejected at Malachor V that Nihilus becomes.
Nothing says that The Exile can't create his own brand of Dark Sideness. Not the Dark Side motivated by Revan's massacres and the Battle of Malachor V, but the Dark Side that is fueled by rage against the Jedi Council and against Revan. My Exile was angry at the Jedi Council's reaction to him, and swore Revenge, and it is this swearing of Revenge that caused The Exile to fall.
If you fall to the Dark Side, Kreia comments that the reason you cut your tie to the Force was because "You had no choice." You didn't want to become Revan's DS pawn (altough you may want to be indepedent, serving yourself) and that you didn't want to die. So you chose the third path, which is to reject the Force.