Suffering and Passionate
You've got to hand it to Antoine—he's a poetic dude. But he's also a guy carrying a lot of pain, and he ain't afraid to show it in his writing.
Sure, he doesn't really think there's any higher purpose in life, but that doesn't make him emotionally cold. Instead, it makes him totally emo about pretty much everything, as he writes:
I shall never rediscover either this woman or this night. I grasp at each second, trying to suck it dry: nothing happens which I do not seize, which I do not fix forever in myself, nothing, neither the fugitive tenderness of those lovely eyes, nor the noises of the street, nor the false dawn of early morning. (10.64)
In the passage we just looked at, Antoine thinks fondly about a moment from his past when he had a wild night with a woman. But now he realizes that the moment is totally gone—it doesn't exist anymore. And according to Antoine's perspective, that means that it might as well never have happened.
Again, though, it seems like the more meaningless he thinks his life is, the more poetic his language seems to get. It's almost like his language is fighting against the absurdity of the world, trying to force it to be beautiful even as it keeps slapping away all the meaning Antoine wants to put onto it.