
Its not that its healthy for the 2 of them to stay together, nor that the thing they are having is a "relationship", its just that he does seem that he cares about him, even thought that he is what he is. And since you said, I personally am an adult and in a long term relationship, I wouldnt like or even let anyone treat me like he treats Min-ki, but its just an opinion on the comic character, people shoudnt find it so personal and real life like.

He doesn't "care" about him, he just wants to posses and control him, he's an narcissistic egomaniac who thinks he can go fuck whoever he wants but if the one person he's steadily hooked up with out of all the others for years does anything with anyone else he beats the shit out of him and treats him like trash. He's the definition of a toxic, chronic abuser and by no means does he actually care about Minki. He cares about him in a sense that by forcing someone to stay subservient only to him and no one else, it boosts his ego and that person falling for anyone else hurts his pride so he physically hurts him. Wonho is such a sociopath I doubt he actually cares for anyone at all other than himself and any manipulative bullshit he might pull when he thinks he's losing the person he keeps under his boot to fall back on is just that, manipulation for his own gain and nothing more.
I don't know, but i can see that wonho actually really loves minki °Д°