Yes, Hak certainly did it. He thought that Su-won likes everyone equally, but it is clearly not the case. Looking at how fond Su-won was of his uncle Il. However, I think about this one Hak can be justified for not noticing, because Su-won pretended that everything is ok.
In Hak’s case it is the dream that Su-won would marry Yona one day and they would live happily ever after where he ignored the big glaring signs that it was likely not going to happen. Su-won made it clear to him that he cannot marry Yona. At least on this subject Su-won was straightforward with him. If Hak listened to him, he might have discovered the reason behind Su-won’s refusal to marry Yona and that something was amiss.
In my opinion, one reason why he didn t bother to listen to Soo Won, was this idealized image of Soo Won. Hak was absolutely sure, that this would be the best turn of events for everyone.
It s not that he asked him to be king, he wished him to be king, he demanded that from Soo Won. Yes, he has never actually listened to him, but he also never bothered to ask him, what Soo Won wished.
Which is funny..even though Soo Won is supposed to be the next king in Hak s mind, he is forced to comply with Hak s wishes.
Hak staying with Soo Won....this would have just come true, if he married Yona and be the next king.
Well, to a certain degree Su-won’s betrayal was a betrayal of Hak and Yona's groundless image of him and their groundless hopes for the future.
As for whether Su-won idealized Hak, I am not sure. Su-won certainly liked Hak very much and admired him, but I don’t think he had an unrealistic image of Hak in his head.
I don t mean that he idolized him in the same way as Hak did, rather he just appreciated the positive traits of Hak, but failed to see, that he might have also weaknesses.
Though I must say, it is not so clearly pictured in the manga...I think you would maybe see that, that he automatically thinks that Hak leads Yona s footsteps, even though it is the other way around.