"It has been a long time since we last met."
"It had been a long time since we had last met."
Do you agree that "had been" is a past form of "has been" and "had met" is a past form of "met"
And I think the second is right but we can see sentences like "It had been a long time since we last met."
What do you think? Thank you so much as usual.
(Not a Teacher)
If you want to be technical, "has been" is present perfect and "had been" is past perfect. "Have met" and "had met" are optional, as the "has been/ had been" sets the frame of reference for the sentence.