Disclaimer: Not mine. Never happened. If these guys were mine, I'd be A LOT more interested in the plot lines of several comic books. Any similarities to any other pieces of fiction are completely accidental. No profit made, written solely for my enjoyment.
Rose knew Tim was gone. She knew that with the startling clarity that few ever knew. It came not from being precognitive, but more from seeing the shadows in his eyes the last time he had returned to the Tower. Unmasked, unguarded. Something had changed him, taken the last shred of whatever it was he had clung to. He had been breaking for so long. Ever since Superboy's death, ever since she had arrived, and even before that. She remembered Dick's never-ending concern for his brother. The fear that his little brother, the third child trapped in the confines of the Robin costume, of the shadow of the Bat, would become the mentor he both loved and despised in equal measure. Rose knew that was not the case.
Somehow she knew that Tim had not followed the narrow path of the Bat. The path where there was only good and bad. Right and wrong. Black and white. Tim had always followed the path filled with shades of gray. The path where there were no definites, no sure things.
To Batman, two wrongs would never make a right. To Tim, they could. He would not be the Bat, but she had never been able to learn him well enough to know what would truly happen should he ever miss a step on the sword's edge he walked. Only that it was unavoidable. Preordained, perhaps. No Robin could ever truly be what the Bat demanded, not even the one who was so close to being most worthy of the title.
Her attempted and eventually successful seduction of the raven-haired, blue-eyed leader had started out as nothing more than survival instinct. To protect herself from complete seclusion. When one slept with their leader, they held an edge, an ace in the hole. She knew that even their stolen nights of pleasure/pain would not keep her on the team if it came down to it, those trained by the Bat had no such loyalty. But she knew it at least gave her the tiniest edge. It at least meant he would tell her to her face if something changed that would mean her leaving the team.
Rose slept in his room the first few nights he was gone.
Even though it had not been his idea to take her in on the team, she had still formed an attachment through their nights together. No matter that only reason she was on the team, the only reason she was even grudgingly accepted, was because of Dick. Because of Tim's devotion to his brother. He was gone though. The overwhelming emptiness of closet and dresser, not that there had ever been much there to begin with, only cemented her gut feeling and she had no doubt that Tim was not planning to return.
And Dick was busy with his own things, far too busy to play babysitter for her.
How long then, until they turned on her? The Titans, for all their claims of being "the good guys" for all their struggles to stay together, united, to live up to the original team, to live up to their mentors' legends, were nothing but a clique, a pack. A pack of rabid beasts that, given the opportunity, would turn on the weakest, the outsider, without a moment's hesitation.
Her place on the team was shaky, uncertain, and no one else who held any weight would back her. It was time for her to leave. To steal away like a shadow in the night, as unreliable and secretive as they all believed her to be.
No one would admit that she left exactly as Tim had.