my favorite things

My personal interpretation behind why the Captain Clark lifeform ate real-Clark after he said, and accepted, that he didn't have to change is that the Captain Clark lifeform represents all of Clark's darkness - his scariness, his violence, alcoholism, inability to make peace with his life or change it for the better. Hince his distorted appearance (a really cool fanart piece illustrated that Captain Clark's facial distortion is similar to the morphing that would happen to real-Clark's face when viewed behind an alcohol bottle). So, Clark refusing to better himself and surrender himself fully to his vices and dark side is symbolized by the embodiment of that, the Captain Clark lifeform, literally consuming him. It's Clark losing his battle with the side of himself that wallows in the worst of him, instead of fighting for his best.

I remember reading the original Euphoria pilot script and going "so initially, Rue was just emo-Cassie with a drug addiction." Thank goodness they reworked that when Zendaya came in and gave us the iconic Rue we know and love.