The problem is Kiss Me Liar. It's like Grayson is a Neurodivergent socially inept victim in his family's stories, but a suave, manipulator social butterfly in Liar that plays people like a fiddle. People come from Liar expecting the Grayson from Liar and are hit smack dab with this person that literally borders on the psychopath with no explanation or change. I've been told that the author actually wrote Grayson first, so its even more baffling for me why they made that bizarre choice.
You are aware that the author writes webnovels?
One of the biggest problem are the manhwa adaptions, for that the author is not responsible.
Grayson was always shown as a grey character by the author. In Kiss me liar, when Yeonwoo thought about Grayson the first time, to his mind came an inscident were he told his ex who wanted to commit suicide by jumping off a building iirc, that she should jump if she wanted to, comming over as a maniac. And also in Kiss me liar we find out that he warned Keith and Yeonwoo about the party at the beginning, and that he was in the end the person who got those alphas off Yeonwoo.
In the extras we see him talk to Yeonwoo, and how akward it was. You clearly saw that Grayson kind of struggled in that conversation, how and when to smile etc. There we also find out that he knew that Keith and Yeonwoo had feelings for eachother, he knew before Keith and he even told Keith half siblings, so they all knew before Keith.
Yeonwoo is always weary of Grayson, while Grayson never really did anything to Yeonwoo. While Keith trust Grayson, and Keith really knows Grayson.
Also in Kiss me liar, Steward has a born manifested in his lab, a serial killer. With stronger pheromones that normal and far more dangerous.
In Kiss me if you can Chase told Josh, that Grayson is only mimicking emotions, that the manhwa adaption also left out in the last chapter.
And in the side stories, Josh will meet a serious Grayson without any emotions shown in his face, not a single smile, no reaction to pain ( at this moment you will know that Josh beating up Grayson before was actually nothing to Grayson, and that he didn't fight back by choice), when he is trying to get Josh for Chase who needs him.

i noticee a lot of debate over Grayson's personality and behavior. it's clear that the dude has psychological issues. perhaps a personality disorder. but it's pretty clear that he has a hard time understanding emotions and the reason behind emotions. him staying with the kid is an example of that. not to mention how naive he comes off. there's no doubt that he gets whatever he wants but it's also pretty clear that he doesn't understand what he should he doing and what not. for example that thing with Chase. he quite didn't understand why his brother was refusing to release his pheromones and he tried to help him. but his disorder restricts his understanding on what is the right way of helping someone.