The MC is exchanged at birth after the real son comes everyone starts hating him. He is in a book he realised when he is dying. He is reincarnated and his father tell him to say sorry to the real son or leave from here. He packs and leave to his original family but they also don't like him. Also the person he likes is singer who gets together with the real son but now he is interested in him
https://www.novelupdates.com/series/i-woke-up-and-was-pregnant/ https://www.novelupdates.com/series/after-the-vicious-cannon-fodder-was-reborn/ https://www.novelupdates.com/series/cannon-fodder-fake-master-was-stunned-after-being-reborn/ Or could it have been an arc from a QT?
https://www.novelupdates.com/series/cannon-fodder-fake-master-was-stunned-after-being-reborn/ This one