Theo started at the touch, shuddered at the contact and leaned back into Greg a little more instinctively, as though he were being threatened. Niki's correction brought made him defensive though, because Greg was nothing like his father and that's who that was, surely, it was, and Theo wasn't thinking about how he knew that.
"Greg." he snapped, and then, gentler. "My Greg."
He wasn't really able to confirm or deny the nickname to Greg, partially because he wasn't sure that it referred to him. He reached up to try and thumb the expression away from his boyfriend's face though.