Why didn't you tell me about it?I should have helped you.

问题描述:

Why didn't you tell me about it?I should have helped you.
这句话是虚拟语气为什么不用过去完成时提问呢?

“你没有告诉我”是一个事实,所以问句不用虚拟语气,用一般过去时就行了.如果非要虚拟,可以这样:
If you had told me about it,I should have helped you.