Our plans to go on holiday together fell through when Jamie became ill.

fell 是动词 fall 的过去式，fall 本意是"落下、下降"。 through 在这里是副词，表示"完全地、彻底地"。 fell through 是一个短语动词，字面意思是"完全落下"，引申为"失败、落空"，特指计划或安排未能实现。