I am confused by the use of ก่อน in this phrase. It literally seems to mean. I must go before, though I know it means I must go now. It seems one would say ต้องไปเดี๋ยวนี้ instead.

Why is the word ก่อน used?

Thank you.

W

Because it means "I have to go before you (the listener)". I.e., you're leaving behind the person you're talking to.

I was about to say I don't have a clue as to WHY, but Soi Mongrel's explanation seems logical.

But as with most things in languages, expressions should always be read in context (this is stolen from a Thai course prepared by Australian National University:)

If you hear "nuu pai kawn na" (mouse go before [part.])

It can mean either: "I (deferential female speaker) have to go now."

or, in for example a laboratory test:

"The mouse goes first" (i.e. before the rabbit, guinea pig, etc.).

(Sorry, no Thai keyboard here).