Question

for your help,i really don't know what i would have done得前面应该加什么？是Had it not been吗？

Answer 1

Had it not been for your help, 综合了两种语法现象：
1 虚拟语态，中文意思：如果没有你的帮助 （其实对方已经帮助他了，所以是虚拟语态）had done是表示的虚拟语态。

2. 独立主格成分倒置，Had it not been, HAD 动词前置

希望能够帮到你！

Answer 2

是的，语感