DS ending: He and Bastila are the Lord and Lady of the Sith, which causes some controversy along the other potential Sith Lords --> Bastila gets assasinated. Revan goes to Outer Rim in grief and tries to gather some power to slay all those who conspired against him.
He will fight with you either if you're LS or DS, as long as he gets his revenge.
LS ending(If Bastila Lives): He and Bastila return to the republic as heroes. But many among the Jedi are uncertain on how to deal with their love for each other which causes a crisis on the Jedis ethical view on love. The Sith use this disarray to distract their presence and assasinate Bastila. Revan goes to the Outer Rim to handle his grief and gather som power for revenge. He also feels that the Jedi are partly guilty for Bastilas death so....
He will fight with you either if you're LS or DS, as long as he gets his revenge.
LS ending(If Bastila dies): Same as if she would've lived, his motivations would be the same. Btw, change Bastila to Carth for the gays and females here