Can someone tell me why MC doesnt like his brother? Im confused

IIRC more or less avoiding death flags so he's pushing triggers away from each other.

I think it’s because he doesn’t believe in his family’s love or concern. He suddenly transferred into a body he’s never seen before and ended up in a family that’s so loving and caring, it makes him feel guilty, you know? Like he’s thinking, “I took over your son’s body, and now you’re showering me with affection and worry meant for him not the real me." But idk that what I just think

He s focused to leave this world. Any interaction which his family makes him stress full and cause him sick. He don't want to bother his current family with his illness.

Identity conflict, low self esteem, dognitive dissonance, derealization or depersonalization, depression, guilty when he already has his own family, mental whiplash

This