Symbolism, Imagery, Allegory
Throughout this book, booze is Jim's special weakness. Sometimes, it just seems like the world is too phony to handle, and the only thing he can do to make himself feel any better is to drink. A lot. The guy couldn't even go a few hours at the Welches' house without sneaking off to the bar, even though he knew that it could jeopardize his job.
Jim doesn't just drink beer out of habit. He's truly in love with the stuff. Just check out this line that pops up when Jim realizes that the pub will close a half-hour later than usual.
His gratitude had been inexpressible in words; only further calls at the bar could pay the happy debt. (5.1)
In other words, the only way to celebrate the late closing time is to buy more beer. That makes perfect sense.
Even when he's at the university Summer Ball, Jim's totally bored, and the only thing that cheers him up is realizing that Mr. Gore-Urquhart is able to get some full pints of beer for them. Jim remarks that:
"It's an unexpected pleasure to be drinking pints at a do like this." (10.34)
Drinking seems to be the only thing in this book makes life bearable for Jim. It symbolizes escape—from the intolerable atmosphere at the college, from Margaret, and from responsibility in general. But drinking too much is bad, m'kay? It gets our boy into piles of trouble, so alcohol also represents the disaster that's been Jim's life up to this point.