If Jack does kill Serenity, than Dark Matter has both as a very good reason to kill Jack and join the Teen Titans. Not because of Serenity, but because of the threat that Jack poses. This is also assuming that Dark Matter doesn't end up killing Jack in this encounter, though I doubt that. Though it may also end up involving Wild Flower an the Pah Zoov Yaj, but that depends on how in-over his head Dark Matter gets himself into.