Nothing could come between us when we were at university; our friendship was unbreakable.

come 在这里是动词，意思是"来到、发生"，表示某种情况或状态的出现。 between 是介词，意思是"在...之间"，表示两者之间的空间、时间或关系。 come between 是一个短语动词，意思是"介入、离间、损害...之间的关系"，指某种因素或行为破坏了原本良好的关系。