"If I knew..." and "If I had known..." (what is the difference, please)

Hi teachers, 

I need your help with the following sentence. I need to complete it by choosing the appropriate option from the options provided below it.

Here's the sentence:
 - If I ____________ you would cheat on me one day, I _____________ trusted you.

Here're the options:

1). knew/would never have
2). had known/would never have
3). either is possible and correct.

I think the second option should complete the sentence,  but I am not very sure of it. By the way, are both "1" and "2" possible there, in that sentence, please? 

Thank you.