Too late — he's already depressed, through no effort on Lucifer's part.

The way Wilhelm's eyes dart away at the precise moment Lucifer pronounces suspicious is a little damning, but he's not letting go of his defenses just yet. He pinches up his face.

"I'm not isolating myself, I'm just..." He puffs out a sigh, buying himself time to think of an excuse. "I can't deal with people right now. Everyone's getting on my nerves."

Which isn't a complete fabrication. It's just that the nerves in question have less to do with his temper and more to do with the nervous breakdown connotation of the word.