Question

i would have come earlier, but i __you were waiting.

为什么选didn't know不选hadn't know?

Answer 1

didn't know

我本该早到的，可我（刚才）不知道你正在等。

you were waiting，这个动作，见了面之后，就知道了，所以不知道这个动作，是刚才的，过去的。
所以要用：didn't know，现在已经知道了。