“但你不在家”常见的英文表述有:But you weren't at home. 或者 But you weren't in.
“were not”是“be”动词“are”的过去式“were”与否定词“not”的组合,表示过去某个时间的否定状态。“at home”是“在家”的常用表达。
例如:I came to see you, but you weren't at home. (我来看你,但你不在家。)
“in”有“在......里面;在家”的意思,所以“weren't in”也能表达“不在家”。
比如:I called you, but you weren't in. (我给你打电话了,但你不在家。)