Eden didn't know why he was hating Cayron that much actually. He had indeed killed him back then, but Eden didn't care that much about it. Sure it was something to be angry about. Cayron didn't need to do that, and they could have just taken different roads and never seen each other again. But Cayron just acted at the moment. He knew that he needed to be apart from him to shine, and at that time, the only solution was to kill him.
And since in the end, Eden was still alive, he didn't see anything to be angry at. He had killed him, but in the end, he was still there, fighting with people, and with a class that was amazingly versatile and strong.
So yes, what he did could have been avoided, so that's wasn't something to be really angry about. But there was something inside Eden that was bottling up wrath. He didn't know what it was, but it was the reason why he hated Cayron that much now.
Do you think he will really do it?