Ed who murdered him unable to let go of the chance to have him.

"That was why I flicked you in the head in the Court. I'd been hallucinating you, a lot. I thought-" He shrugs slightly. It's clear what he thought.

There's another pause and then Ed looks back to Oswald, giving a small, tight smile. He doesn't say anything, because the anxiety is churning so high that he feels sick, the anxiety of saying as much as he has, of being convinced that if he tries anything more than this friendship from them, Oswald will leave, or die, or leave and then die. The anxiety of losing what he has. That he'll kill Oswald without meaning to.