Why?

Because Muyeol (his “brother”) told him like 10 chapters back that Min-chan isn’t a true identity. His soul is incomplete and isn’t really his to begin with—it’s just fragments of Seoho’s soul, but not all of it. Seoho allowed his soul to be shattered in order to save Bihwan. Muyeol is planning to transfer all the fragments of Seoho’s soul into a different vessel, which would mean Min-chan would cease to exist. When he looked at Min-chan’s core, he saw that it was truly cracked and wasn’t whole

Omg thank u I feel so dumb