Suppose that I wanted to borrow money from one of my friends. I went and saw him in his home. He has accepted my offer and has lent me the money I wanted. now I want to tell him:
If you haven't lent me money, I would be very sad.
is the above tense correct or should I use past perfect?
You should use the past perfect tense.
Because you already borrowed money from him. These sentences are truly hypothetical and unreal, because it is now too late for the condition or its result to exist.
The reality is the opposite of, or contrary to, what the sentence expresses.
If you hadn't lent me money, I would have been very sad. (But, he lent money)
