Isn't it unfair for Killua to still be mad at Gon? Gon was going through a suicidal breakdown, didn't want Killua to go down in flames with him, apologized both on and off screen/panel about it, and if Killua didn't make his full feelings known, how can he still hold that against Gon? I mean, it sucks that he's already being left behind AGAIN by someone who he thought cared about him, but for Killua to still hold a grudge is so harsh

ohh this is a very good question! 

the short answer for me is no, it’s not unfair.

the long answer is that feelings aren’t fair or unfair, they just are. killua, or any person for that matter, can’t really control the way he feels. moreover, he is a child with little to no conventional socialization, he has no idea how to handle his emotions, and that tangle of intense love and hurt he feels towards gon probably drives him nuts as it is, without the added layer of trying to reflect on those feelings.

that said, boy did killua screw up. his relationship with gon is a textbook case of communication issues with a spoonful of codependency (because killua has never in his life had a relationship that wasn’t codependent, kind of hard to get rid of that pattern on your own). killua’s hugest flaw is that he cannot talk to save his life. he is very good at expressing emotions of minor importance, like irritation, surprise, excitement, but if you dig a little bit deeper he bristles and closes up. gon gushes about how much he appreciates killua? blush and devalue that by calling gon embarrassing. deeply disturbed by the fact that gon clams up in the face of killua’s request that goes against gon’s selfish wishes? smile and sweep everything under the carpet. mad at best friend for shutting him off and saying some really rotten things to him? killua was so Enraged that he faced off his family, which is the only thing that truly terrifies him, kidnapped his sister and negotiated with his abusive brother just so he could heal gon, All for the sake of eventually bitch-slapping him and giving him what-for. and then killua sees gon, all healthy and smiling, and all he can muster is a half-hearted and jokingly angry “well, weren’t you mean to me!”

no fucking wonder all gon said in response was “aww i’m so sorry killua :( :)”

gon, though, is not completely innocent here either. while i do love to rag on killua for being a closed off reticent brat, especially in contrast to gon, who is Much more healthily communicative, gon has his own issues with interpersonal relationships. his Main issue is that his relationships are never his first priority – or, should i say, they are only a priority as long as his friends’ goals don’t clash with his own. don’t get me wrong – loving yourself and understanding that you are your own most important person is good and healthy, but gon is deeply selfish and self-centered with an all-or-nothing mindset and no idea how to meet people half way. and since his sense of self revolves around being Powerful, Power is what he puts on the pedestal. and Bingo! it’s exactly what compromises his otherwise impeccable social skills and emotional openness. Power is the only thing that fazes gon – all the times i remember him crying was because he felt weak and sorry for himself. and the one time he isn’t honest with killua is when he is feeling resentful towards him, because boy howdy is gon jealous of the fact that killua is stronger than him, and oh how carefully he hides that embarrassing secret. i firmly believe that gon harshly refused killua’s help not so much because he was worried about killua being caught in the cross-fire, but because of that very resentment telling him that killua, his so much more composed (is he though?) and experienced friend, thought he was weak and needed help achieving his own goal.

so now we have these two emotionally inexperienced children trying to have That Talk under the world tree (i’m begging you togashi that was so symbolic and tongue-in-cheek at the same time). the talk where they should come clean and apologize for everything — and guess what? it doesn’t work, because apologies only go so far if you don’t discuss what you are apologizing for (hint: they don’t go anywhere, period). gon doesn’t understand the full scope of how much he fucked up both because he is self-centered and it’s sort of outside of his mindset, and because killua never told him how gravely he had been hurt by gon’s actions. it’s all made even worse by the fact that gon doesn’t know that he was practically dead and killua dragged his sorry ass out of hell itself, all because killua insisted that no one tell gon what had actually happened. 

that apology really didn’t count, did it. it didn’t even come close to counting.

tl;dr the boys both screwed up big time, and the only remedy is Talking. so much talking.