It's not so much of a drinking problem as it is a general impulse-control problem. It doesn't help that he keeps overestimating what he can handle ever since becoming NEO. With higher confidence and gaining a safe environment has also come more indulgence. He'll greedily take alcohol, food, sex, shiny objects, or whatever else he wants in abundance because he deserves it, but also because it's simply too hard to resist. He gets anxious if there are things around him he wants or needs and he doesn't take enough of it. On the other hand, he also gets anxious if he has too much because he might lose it. All that comes on top of having a highstrung and strongwilled nature to begin with. The other issue is that Tenna has a very hard time saying no to him.