They had a serious bust-up about work schedules and ended their relationship.

bust-up 是复合名词，由动词 bust（打破、破裂）和副词 up（彻底、完全）组成。bust 本身是 burst（爆裂）的非正式变体。 bust-up 在口语中表示"激烈的争吵"或"关系的彻底破裂"，常用来形容导致关系结束的严重争执。