There were aspects of being alone that Beast Boy didn't enjoy; he was left to deal with his thoughts. He knew he could go to the Doom Patrol if he wanted or even, dare he think of it, back to the Titans, but he didn't want to. He knew that he would tire of pretending too quickly. He would grow sick of Mento's attitude towards missions where the lives of his team don't matter as long as they are successful in their task. He would bore of Elasti-Girl's overbearing nature of how she would treat him like a little kid with no knowledge of the world.
So, he didn't go back to anything. He lingered on the streets. Rough sleeping on the streets he used to patrol. Wearing masks to keep his identity hidden because he knew full well that his skin colour was a giveaway. He rummaged through bins, occasionally finding a carrot stick or mouldy lettuce that someone hadn't eaten. Shifting into a mouse, he would drink from puddles. He could feel a sickness in his bones, in his mind, that had been a long time coming.
He wasn't a criminal. He never stole anything. He only hurt villains, leaving them unconscious for the police or the Titans to deal with. Initially, he had wanted to leave them tied up, but with such limited resources that wasn't an option. He lingered in shadows, only pouncing when the Titans were late in showing up. He was gone long before any of his former teammates, former family, could arrive.
He couldn't keep this up forever. He was barely managing now. He was constantly plagued by constant headaches; his ribs constantly threatening to rip out of his skin whenever he shifted. His body was exhausted, even breathing felt like an effort. He found an alleyway to make his peace with the world. He watched people dash past, barely acknowledging his existence. Yes, Beast Boy would die quietly. Alone.
However, in what we expected to be his final moments, he was met by a familiar face. One which would make the Titans' taunts feel like child's play. He had nowhere to go and no way to escape. No one was coming to save him, he'd made sure of that by his own actions.
So, Beast Boy returned to being nothing more than a lab experiment.
