I actually thought that their budding attraction was very believable and handled rather well in the first episode. They're not in high school, both adults in their 20s, and what they very obviously did was flirting. It may have been subtle, but even FLs friend caught on it and teased her for it. So while ML was definitely impulsive, it wasn't entirely out of the blue. After he stops her from leaving/grabs her wrist (it didn't look forceful to me btw), they look at each other for several moments in close proximity before he kisses her. She could have stopped him at any time, turned away or told him, 'no' very clearly. Even though she breaks the kiss momentarily, her confusion upon wavering is apparent, and she kisses him back. As she is leaving she tells him 'I have a boyfriend', but he doesn't believe her, because she reciprocated the kiss. Telling her boldly that he wants to sleep with her, is definitely unprecedented in K-drama land, and it would definitely count as sexual harassment had they not just made out in a backroom in the hospital lol And that steamy kiss, was very obviously mutual. I mean, yeah, he's extremely straight forward in sharing his attraction, but I've honestly seen and heard much worse in real life. He doesn't get handsy. It is obvious he thinks she is single and lied about having a boyfriend, until the car stops by to pick her up, btw.
So while I think he does have an infatuation with her and boldly and somewhat childishly goes after her, I don't see it as a big issue as far as consent goes. Literally none of the guys I've been with have asked me 'is it okay for me to kiss you', before our first kiss, nor have I, if I was the one initiating. I mean, most kisses just happen in the mood. Obviously you should be able to read your partner and give them time to pull back if they're not on board, but 'asking' for permission seems somewhat strange to me.