He doesn't know what'd he say. What could he say? What do you say when you've realised you've abandoned someone in another universe, even if it wasn't intentional at all? No, he couldn't control it. There was nothing he could do. If he had let go himself, they would both fall into the void, lost forever. In retrospect, maybe losing himself in the void would've been better than this, better than being alive, being aware of everything around him. Without her.

He doesn't know what she'd say. Would she be angry with him? Would she tell him how much she's missed him? No, don't be stupid. She has a new life now. With her mum, and her dad, and Mickey. There would be more adventures out there for her, he knows it. She's not going to be just a shopgirl and eat chips all day. She's going to carry on her life, meet someone new, and just live. Like humans do. Wait for normalcy to come back in the form of a new career, a new family, and a new... companion?

Why do his hearts want to stop beating just thinking about that possibility?

He is standing in the TARDIS. Alone. He's never realised how huge and roomy it is. This would never be the same. He's had so many companions. Oh, so many. When has he ever used a supernova just to leave a proper goodbye? He needs to see her face. He needs to hear her voice. If he were going to spend eternity without her, he needs to at least know that she will be okay. His hand begins to shake, only the slightest, as his finger reaches for the button. "Hello, Rose..."