Then let me make it up to you.
What does the above sentence mean?
It means “let me repay you” or “let me make it better”. It means I am sorry, please let me know what I can do to restore our relationship.
boy, is it going to hurt.
What does the above clause mean?
“Boy” here is just an intensifier, like “wow” or “man” or “gosh”, so it means “This is really going to hurt.”
Is it an intensifier or interjection, Luschen? Intensifier, in modern grammar, is an adjective (to be more specific, a prenominal).
Yes are are right, interjection is the correct term. Thank you!