The use in that sentence is a little awkward, but it works - I can understand the meaning. In that sentence, "past bearing" would be an adverb (pretty sure), as bearing is a form of the verb "to bear." It's a different way of something is unbearable. More commonly, it would be said like this: "Collage was bad enough, but now it's unbearable." "College was bad enough, but now it's beyond unbearable." (in this sentence, beyond unbearable means that it is significantly worse than a level that would still be considered unbearable)

Here, "past" means "beyond".