Title says it all. Kurapika was completely absent while Gon was almost dead. In the anime, it showed one flashback to Kurapika sitting on a chair, but thats all. Was this explained at all?
Kurapika was throwing a funeral for his dead family/clan members of the eyes he recovered and who knows what kind of stuff he went through to get them.
Also the condition Gon put himself in could make him even more depressed as Gon much sacrificed his life to get revenge especially when Gon was trying to stop Kurapika from being a killer that someone as pure hearted as Gon can even become a monster. Killua was upset since he couldn't fight Neferpitou with him side by side. Now imagine Kurapika who had no clue about the Ant's existance and what those two were going through and him being with them could of possibly prevented all the events till now from happening.
Also Gon partially got the idea of making a severe vow from Kurapika.
Basically a friend he made after being alone for so long went down the same path as him.