Remember that the alternative, was that he be imprisoned in the tower and not let out. So honestly staying with Lysbet was the best option, because at least while she was around, Lister would not harm him. Lysbet was also aware her brother was in love with Sylhan as well (abusive kind though it was), he also would never kill him.
Yes, but that doesn't answer my main question which was: acknowledging it WAS one of the few/better options for Sylhan, why did Gjord not intervene at any point while he was under Lysbet's supposed care? Keeping him alive was the bare minimum, but letting him be constantly abused by Lister and his memory deteriorate to such a degree, surely he could've applied some further pressure on Lysbet about her brother's treatment of Sylhan (like remove him from serving him) and find a way to switch the medicine sooner without them catching on. Ofc he couldn't kill Lister bc he'd lose his leverage, but for someone who boasts how his desperation and sole motivation has been regaining Sylhan's rightful status and kill everyone who's ever wronged him, leaving him for 2 years in that state doesn't quite add, even while taking into account all the obstacles and limitations.
Idk if Gjord in the novel is less considerate than the utterly romantic and dedicated character portrayed in the manhwa and these events match the novel's characterization or there's some other missing part (discrepancy between adaptation&original or hidden info not yet revealed), but the fact that this hasn't been addressed in the plot leaves me perplexed.
I think you're forgetting that no one liked Gjord. His status wasn't high enough at the time AND everyone knew he had a thing with Sylhan, so his allies were few (and the fact he just said every ally was killed, any possible help in Khallak to truly look over Sylhan), not to mention he went to that war for YEARS and FAR AWAY because of that deal and wasn't allowed to get back to Khallak until it was over. He had no means to spare to check if the deal was being followed properly. As he said, it was the only thing he could do, trust on the deal.
And yeah, it was a stupid decision, but it was literally either leaving Sylhan with the Glenberg's, nowing they would not kill him and prevent life threatening situations, or leaving him in a tower as a common prisoner, where he could get abused in many forms or even killed by his old political enemies. As we saw, it wasn't a good decision but, given the circumstances, it was somehow the best
I've considered everything you mention and at first glance it seems like a cohesive conclusion, but it has too many inconsistencies imo (at least so far).
-Gjord being away at war doesn't mean he couldn't use sorcery or messengers/spies at some point. He HAS been shown doing exactly that to interfere, communicate and influence happenings in other areas. Being at the battlefield made it harder, but not impossible.
-He didn't have vocal allies, but he did have secret ones. Not that they'd easily stick out their neck for bettering Sylhan's state at that point, but they could provide indirect assistance. I don't believe that it'd have otherwise been possible to hold Lysbet's secret over her head, who would trust his words back then when he hadn't yet become useful or harder to get rid of as "a hero" in the war. Most importantly though, he had connections who were indebted to him in Khallak.
-In the first chapters in particular, Gjord kept repeating how he relied on Lysbet's correspondence while he was away and trusted her that he was safe and being taken care of. Even going as far as to complain that he was at war but Sylhan had it easy within the castle. There is no way he could be such a mastermind to end a 20year war in his 2year involvement and come back to Khallak with political schemes already planned ahead, BUT his intellect draws a blank at guessing how Sylhan is being treated by his literal enemies at home and never bothers to check in on him through someone he trusts more than Lysbet's words? Are we supposed to believe that makes sense?
-His deal with Lysbet hung in the balance of him being sent to the civil war to keep him occupied or killed and her ensuring Sylhan stays alive in Khallak in the meantime. I think she expected him to not return, much less that it would be as soon and as successfully as he did. It's what her actions tell me once he was back, panicking and eventually even having Sylhan taken away to Glenberg to be married to Lister. It put Sylhan further from the throne, but it also meant a huge risk for Lister's life (he'd become Gjord's target), which Lysbet might have been willing to take at that point; forsaking her brother, but ensuring Kurstin will succeed her and still have a house. That's why she struck a deal with the general to lure Gjord out of the castle and he'd offer protection for her son in turn.
All of which leads me to believe that based on the plot so far, the author just wanted for Sylhan to have suffered in quite the dramatic and seemingly inevitable manner in the hands of Lister, while still making Gjord's character quite overpowered and trusting nobody would really bat an eye at these plot holes
Now, if it was to be revealed that Gjord planned for it that way, it would be cruel, but it would at least add up and I'd appreciate the writing. Something like they'd all gravely underestimate his objective, his involvement in Sylhan's plans for the throne and his strategic planning/connections. He planned on minimizing himself as a threat just to the degree where having that secret does hold as leverage with the Glenbergs, but not pushing any further than trusting Sylhan will be kept alive. That way he could buy time and set his plans into motion, without much interference from others. And a major part of that was sacrificing Sylhan's physical and mental state for 2 years.
Anyway, it's not like this is some hill to die on. It's still a good story and I'm not gonna form an opinion on this part until it's completed. But since it's a plot with this much intrigue and detail I couldn't just let it go lol
Sorry, something isn't clicking for me in ch. 90.
So, Gjord left Sylhan in the care of Lysbet, believing that she won't harm him because he knew her secret: that Lister had colluded with the general to let his troops in Khallak unchecked. Which led to the last Lord of Khallak being killed and Sylhan having his status removed and turned slave.
Why in the world did he think that it was a good idea - EVEN as a last resort - to let Sylhan close to Lister when he essentially led to his downfall and even a fool could guess that Lister would try to take advantage of that?? ESPECIALLY since Gjord knew of Lysbet's declining health and her desperation in protecting her brother, he must've predicted that even in the best case scenario she wouldn't be able to or willing to truly keep her word and keep Sylhan safe; not from her brother nor from the new Lord of Khallak.
So, if Gjord cares oh so much for Sylhan, HOWWWW did he not intervene sooner to at least keep an eye on Lysbet and keep a tighter leash on/threaten her any time she failed to adhere to their agreement??? I understand she was likely one of the very few choices he had to ensure than at least Sylhan isn't removed from Khallak and so he has a better chance at taking back his former status, but you can't tell me THIS was the best he could do, given the informants and sorcerers he had in his disposal. Letting Lister run loose and abuse him over 2 years, while his memories were being suppressed.
Unless I'm missing something, this seems either like a glaring plot hole or that Gjord is hiding something.