此句的文法是否錯了？

I thought you had gone home for a long time. = past perfect tense

I thought you went home long time ago = past tense

I thought you have gone home for a long time.

你的句子文化當然錯，但錯並不在時式，而是用了ago
ago是與現在有關，即從現在計起的以前，如：3 years ago即由現在計起的三年前

既然I thought已經表現，參考時間不是現在，以是過去，所以，就不應用ago，而是before

I thought you had gone home a long time before.

希望幫到你！

I think the most correct sentence is :

I thought you had gone home a long time ago is correct

I thought you went home a long time ago. It just have different meaning