The first is in the past perfect tense. I believe you have a past perfective tense in Hindi. In English, it's only used to compare two things that happened at different times in the past.
So, you use the simple past, if something has just occurred to make you say that.
I didn't expect this from you.
You say the first version if something has happened in the past more recently than the what the statement applies to. So you have already changed your mind about the person.
I had not expected this from you, until I found out what sort of person you were.
That means that since I found out what sort of person you are (something that happened in the past), I have not been surprised about it (Another thing that happened in the past, but more recently than - and as a consequence of - the first event).
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