Sometimes you need to be honest. You don't have to be brutal about it, but you need to put it out there. "Look, I really need some quiet time to prepare for this next class. So, excuse me while I go somewhere quiet to focus." I don't see that as dishonest because that quiet time is needed to prepare for some classes and regain your focus. It is not rude to excuse yourself from that unwanted conversation.

There are introverts (like you I assume, and like me to a degree) and extroverts (like the person you mentioned). People have many dimensions and there are differences between introverts and extroverts and how we interact… The world is full of all kinds and you have to be able to deal with both kinds. When the other person is getting on your nerves, you need to be able to communicate your own feelings - but not judgmentally because that shuts down communication. Most of the time people just make a plausible excuse why they have to go and just go somewhere else. But be aware that an extrovert needs other people and being told you don’t want to be around them hurts. So diplomacy is required.

you could have just said you have somewhere to be and gone to the library.