Now that I've read this

Like I'd be devastated if she forgot me after everything we've been through

Her trauma response seems to be to just push all of it down and keep it away and his seems to be joking about it not being all that serious

Your sometimes brain tends to block out things like bad childhoods since they can be self destructive. But i'm glad Yeonwoo notices that deep down, Haesol still cares for her brother that's why he's trying to patch up their relationship