gon:
-losing you
-math, yeah, probably math
-losing friends *cough*killua*cough*
-you

Killua:
-illumi
-you/losing you
-losing alluka

Kurapika:
-the spiders (phantom troupe)
-phantom troupe killing his only friends, mostly losing you
-knowing your in a dangerous mission without him

Hisoka:
-not taking his victim's virginity
-losing track of his 'ripe fruit'
-you

Illumi: (my auto correct finally learned how to spell illumi instead of Illuminati)
-you
-losing you

Chrollo:
-losing his family/troupe members
-losing you

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If you notice, hisoka's part has no "losing you"