I don't get this movie. What is the message? What was the point of the subplot between the student and the teacher? Why did the Ukrainan rat him out? I was waiting for a climax, but it never came. This movie was like having sex and then pulling out at the last minute.
The movie explores messages about
1). Crime (is the protagonist sympathetic or not?)
2). Family & friendships
3). Regret / Redemption / Lives not lived to full potential / the roads not taken etc.
Your other questions:
1) what was the point of the teacher subplot? To show that everyone, including respectable teachers, is capable of doing something bad, just as Monty did
2). The Ukrainian ratted him out because the police were after him. The purpose of the Ukrainian’s ratting him out was to show that Monty made the wrong choice in friends. Remember that Frank and Jacob spoke about how they hardly saw Monty nowadays. Monty used to spend his time with people like the Ukrainian (the opening scene where he finds Doyle; it’s the Ukrainian with him). The purpose was to show that Monty made an error; he screwed it all up; he took the wrong path in life. He should’ve stayed with his true friends - Frank and Jacob (who would have never ratted him out) - instead of his false friends, like the fat Ukrainian