When Soubi looks at Ritsuka, he is reminded of himself. Restricted, chained, and bound- his eyes impassive, yearning to satisfy those judging him.
No, they aren't the same. Soubi was taught to empty his thoughts to a plain that pain didn't exist within. He is frightened by it, yet drawn to its addictive, destructive embrace. The definition of pain was stolen from him.
Ritsuka is eager to please, to prove his worth; for Seimei, for mother, for the truth. Soubi is both impressed and tormented by this fact. He wants his sacrifice to truly feel, for Soubi never got the chance. The memories he wants Ritsuka to create are happy ones, ones without pain.
Even if Soubi therefore isn't a part of them.