Oshi no Ko - Episode 2 - Third Option - Reaction and Discussion! 

As I see it, Aqua "died again" when Ai was killed, or at least part of him died that day. As he said in the last episode the only reason he is still alive is to kill his father, he doesn't care who he has to manipulate or trick to do it. Of course he loves Ruby and wants to protect her, but his hatred of Ai's murderer has turned into a hatred of everything related to the world of stardom and more specifically idols, that is why in his mind there is nothing wrong with destroying her dreams in order to get her away from that world; in fact the only reason he seems inspired to act is because it was his mother's dying wish for him. I honestly think that the comparison some people had made of Aqua with Light Yagami is very accurate: he has a ultimate goal, which for him is completly just and morally correct, and he is willing to do everything to complete it, no matter what.

Ruby is gonna take the back seat. Aqua supremacy incoming through out the whole season.

Sadly he had to leave because of the internet flaming. Being a manager of an idol group and letting an idol die is akin to losing your life in that industry. And yeah there is one more reason.