This may cheer you up, hearing about someone else getting screwed in the past by 'clever' bosses - when I was 18 or so still working at my first job (a pet store that rhymes with Met Ko) my boss pulled me aside and informed me that my schedule was making it difficult for them to keep me on. I was working 4 10 hour days at the store (Sun, Tues THurs and Sat, 7am to 5pm each day) so I could spend M W F doing a near full course load at college. We had agreed upon this schedule early on in my college carreer and it seemed all was going well, but I guess the 'new' boss (who was a kind voiced, charming man) didn't like my liberties and told me they were going to have to fire me if my schedule didn't open up. He played on the fact that I was afraid to be fired by telling me "you don't really want FIRED on your records, do you? it'll make it very hard to get another job in future..." so he basically pushed me to quit.
Now as an adult I realize he not only got rid of me but made me ineligible for unemployment benefits which, as a direct result caused me to be unable to keep up a full course load at college while I searched for a new job.
It happens, but YOU have to be the knowledgeable one, and just like me I bet if I turned to him and said "Well fire me then, if you want me gone, so I can collect unemployment while I find a new job" instead of "Oh gosh I don't wanna be FIRED! Alright, I quit, see ya :-(" the turnout woulda been different.
You can't go in there screaming and you gotta watch that temper, but if you let your boss know you mean business and you're tired of being dicked around with a turkey and zero PTO he will NOT want to get tied up in litigation.