We didn't even see the real Grayson sadly cause of such a bad Adaptation, the real reason he left was that the situation and fire was very serious and Grayson was telling Dane to turn back but Dane didn't turn back, Grayson was planning to drag Dane back by force but we all know Dane he ran away leaving Grayson alone, also Grayson had an Order from willkins that he must obey all commands of dane and when Dane told Grayson that he is a liability and told Grayson to go out he obeyed Dane and house started to collapse so Grayson did what any rational person will do.
oh?? the chapter didn't reflect the severity well enough then...at no point did I feel like someone could be gravely injured or lose their life like Dane, even escaped all the suffocating smoke without his mask (I know the author said the fire hadn't reached the attic by then).Maybe the author would hint at Grayson's internal thoughts about wanting to drag Dane out by force like you said because that's pretty important in this story's core aspect as Grayson didn't look like he cares an ounch for Dane in this chapter. Also that must have been a huge sized exhaust-fan :D
Why? Because he isn't a piece of trash like you?... he'd save you, too, again in a fire like that out of duty, no less.