Alcoholics drink to get through the day, Wyl is drinking because the veneer of his heroic persona cracked for a moment, bringing up his past. I don't remember which fight triggers that scene, but they're both goblins that knew him before he was the Blade, and were responsible for whatever event drove him into a pact with Mizora.
I'm not sure what people consider inconsistent about him.
Well, to be fair it's not just one drinking scene. He's continually swigging from a flask pretty much every time we're in camp, though now I'm looking more closely at him I see that the flask is often an invisible one. I'm sure that you used to be able to see it in his hands in the idle animation! (I'll leave aside my suggestion that thinking of him as a drunk, albeit a functioning one, makes sense of a lot of the elements of his behaviour: I accept that's very much a matter of personal interpretation.)
In terms of inconsistency, my take is that, eg, sometimes he seems to mean his Blade of Frontiers schtick whereas sometimes it feels more like self-parody, he seems to want to help people but when it doesn't fit with his aims he's willing to throw them under the bus such as his dismissiveness of Barcus's plight at the windmill or how far he's willing to go with Liam, then there's the fact that he often comes across as a jovial soul but then suddenly displays disturbing wells of hatred and anger. I don't think that these inconsistencies (contradications? tensions?) are bad - real people are often inconsistent. And it makes a lot of sense that he's conflicted about his Blade of Frontiers persona given he feels it's constructed on a lie, and that he is truly desperate about breaking his pact and willing to go to almost any lengths to find Mizora and deal with it, and he can be honest about wanting to help people without being completely selfless. And it's perfectly plausible that an apparently jovial person could be capable of sudden mood swings to great anger. Larian can certainly develop his character in a way that makes sense of these tensions in him, I just meant that they make it hard to get a handle on him right now, and I'm guessing that's at least partly because he could go in different directions depending on the choices we make.
