To the people confused about the 'not serious enough' comment, I think she's trying to cope with her feelings of inadequacy (27 vs 19yo, her fickle nature that makes her very volatile, the contradiction of being in love while knowing your lover will leave soon) by telling herself she's just not that serious so it hurts less when the separation (supposedly) happens, she's basically building up her defences, it can also be seen when she says she's just a prankster terrorising kids, turning her own feelings into a joke lessens the blow
Thank you for the translation, can't wait for the next chapter