It does, in fact, get worse. Not that it isn't to be expected, but there's no warning (which isn't really expected, either.) It's powerfully sudden, Dean left with the sudden musky taste of Lucifer's come on the back of his tongue. There's nothing to do but swallow, doing it hard and fast around the head of Lucifer's cock, getting the whole thing over with as quickly as he can manage. Squeezing his eyes shut through the brunt of it is all Dean can do to manage, trying to blank out the image before him.