Why the crying?
The movie maintained a certain emotional detachment throughout and, I thought, there was no sad event/resolution?

I'm not even sure of Ryan's character was fired when he went to see the principal (and a substitute showed up in class the next day), or if he merely called in "sick" that day.

At the end, his shaving off of his beard while his favorite student sat on the couch seemed to be an indication that he would be getting his shit together. Therefore hopeful?

Maybe the sad part was when his favorite student decided to earn a little $ delivering dope, and Frank made sure her second delivery was to Ryan in that motel room?