He touched his head without really thinking about it, it came naturally to him. So him being so naturally affectionate to him freaked him out, because at this point in the story he's ignorant to his own feelings. So because he's freaked himself out, he's basically using the gf(s) as a rebound to bring himself a sense of normalcy, plus the added bonus of the fact that it makes Joonghwan jealous

i dont get it, why did he touch his head then the next day got a gf? its so confusing, and he keeps raping him and forcing him to do things its just makes me think why