Responses
Yes, he kept seeing habits from this new Sihyeon like the peculiar way he holds a cigarette, how natural he feels around him, the drama scene where he perfectly acted like.Hajin,... Then it was all confirmed when Sihyeon visited him while he was drunk and, thinking he was dead drunk, revealed himself in a "don't torture yourself over my death, just think I ran away if it makes it easier for you" way.
So black haired guy knows hes not the og sihyeon? (Sorry i keep forgetting the names)