[How is he supposed to know? Sizhui looks at the ground, wide eyed, as he calculates what's going on]
If he was with this person, were you still friends in this illusion?
Other options:
no subject
[How is he supposed to know? Sizhui looks at the ground, wide eyed, as he calculates what's going on]
If he was with this person, were you still friends in this illusion?