You should read the chapter again, Killua and Gon parted, but they didn't want to leave each other.. Gon said i still want to stay and venture with you but Killua is like you should go talk to your Dad... When they parted they didn't seem happy at all, i didn't see them smiling.. It's not like they're gonna part forever, they're just a bit reluctant thats all. I would understand them to be more emotional if they're cutting their ties, they just have their own business to attend to thats it...
Having three emotional reunions or partings would be overdone but togashi didn't want to take that route because he didn't need to.. =[]