It took a long moment for it to sink in completely. Terrence didn't even move while it happened, didn't pull away from her hands on his temples. The touch was nice, comforting, though of course it didn't really do much of anything. Except remind him that she was real, this was real, even if everything else inside his head wasn't.
The first real, strong emotion to come through was frustration, anger, boiling quickly into rage. Somewhere deep down he was aware that it stemmed from fear, fear of being controlled by anything or anyone, fear that he usually called hatred. It hadn't happened to him since he was a child, since the last time anyone had tried to get into his head before he'd learned how to protect his mind, when he'd just hated it so much that he set things on fire around him and forced the other wizard to break the connection.
He sat up suddenly, unable to stand the gentleness of the touch any longer. He didn't really have a plan for what he was sitting up to do, though, so for a moment he stared at nothing, at the wall across the room, since that was what he happened to be facing. Fuck.
It changed everything, but at the same time, it didn't change anything. The only way he was allowed to know that secret, the only way he could get off the potion was to take the Mark, as he'd already decided to do. Except, it wasn't entirely true that it was the only option - there had been something in that memory that he'd vaguely registered, the possibility of vouching for people she trusted to be off the potion, as some sort of consolation prize - but that wasn't really an option. The idea of being indebted to Ella, having to watch his step once he was off the potion and had Merlin knew what kind of opinions about the government in order to keep them from killing her, was worse than the idea of that Mark on his arm.
No, his free will was his own responsibility. He didn't have it now, hadn't had it since the Dark Lord had come to power and started feeding him some kind of potion to keep him from being dangerous. If he became dangerous once he was out from under, once he was Marked by the Dark Lord, then the Dark Lord would regret it.
"It doesn't change anything," he said, giving voice to what he was thinking. He was still careful to keep his words vague, aware somewhere in his mind that it could never be said aloud or written down, that the specific information had to stay in their heads. "Everything, but nothing. Not really."
He got up, heading for his closet. It wouldn't help anything to leave, but he had to move, had to find a way to let loose everything he felt before he burned the flat down around their ears.