So this is how the break up between Noelle and Cas goes. Noelle knows that with his career comes travelling and groupies and she’s not secure enough to handle that so she breaks it off despite her not really wanting to. She doesn’t hear Cas out and decides by herself to do this hence his curtness in MCLUL. She thinks that her insecurity and anxiety will be a hindrance for him and his career and she knows it will effect her badly. Not wanting him to blow his shot she ends things abruptly in the middle of the night by a phone call. She refuses to answer his calls or texts after that and then, without a word, moves away to start college.
Added note: In the multi-candyverse Noelle and Cocoa also break up before college though it’s more of a mutual thing realising they are two very different people.