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I think the mc just gave up trying to get away from him, he tried many times and failed many times, stalker psychologically manipulated him, now he has Stockholm syndrome from him, also I never saw a mention of anyone who can be close or be friends with mc, maybe this is why he got Stockholm syndrome from him since stalker was the only one constantly with him by days. Since he gave up he I guess just came with the terms of " this is it, this is my life now " like that
Everytime I read their mangas I'm always suprised how complex their work is