From what I remember mostly, he did actually have feelings for mc but there is a reason on why he’s fighting mc. He’s in his body since mc realised and recognised him as his past partner when they met again a few more chapters in the novel. I forgot on why they were fighting to be honest, but it had something to do with the evil organisation ( yknow the one that keeps sending clones of colonel to mimic ) and his past partner now involved with that organisation. In this latest chapter, he or the past mc’s partner might be the one who teleported him when he was in the bathroom ( tge mysterious guy? ) I don’t remember his name to be honest, but I do know he’s also involved with the organisation somehow ( from what I remember, again take this information like a grain of salt. It’s been LONG since I’ve read the novel. )
I think he was jealous or something, I think he did say or show his intentions on why he became evil. I do know that when mc and kang muhyeok went into a secret shit bunker raid thing, they were able to find experiments and one, his past partner being involved in that shenanigans. Idk if he is also an experiment or different one

is this guy the one who will be fighting mc later on ( into the novel, forgot tge dude’s name ) or is it the partner he “ lost “