are there any misunderstanding and breakups between the leads?
not at all! no toxicity happened here, they are a healthy couple. gongwon (the main couple) were there for each other until the end, not until kijoon's mom went to him and said that he should follow her to Canada. while seoyoungjoo (the second couple which are also the leads) they only went canon in the last episode where seoyoung finished her exam for university. basically youngjoo waited for her