The Order sends Draco to be Marked. He's a Malfoy, it's expected.

When he comes back, there's something off. Draco doesn't move right, and waits too long before he speaks. But it's nothing Harry can pinpoint, so he doesn't tell; instead he catches Draco alone.

"I was afraid for you," he says, and touches Draco's face; Draco, who hates him, would never have permitted it.

Later, he tells the professors that what was sent back isn't Draco. When Snape asks how he knows, he closes his eyes against the memory of hands on his skin and whispers, "I just do."