In the evening, it got colder than it [had been], so we reached home shivering.

had been 是动词 be 的过去完成时形式，表示"曾经是"或"之前的状态"。 reached 是动词 reach 的过去式，reach 的意思是"到达"某个地方或状态。 reached home 表示"到家"的意思，指完成回家的动作。