Eine Frau he's wed, astray for so long in Berlin (3,11)

I believe the answer is:

auf wiedersehen

I'm a little stuck... Click here to teach me more about this clue!

'so long in berlin' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'eine frau he's wed astray' is the wordplay.
'astray' indicates an anagram.
'eine'+'frau'+'hes'+'wed'='einefrauheswed'
'einefrauheswed' is an anagram of 'AUF WIEDERSEHEN'.

'for' acts as a link.

Can you help me to learn more?

(Other definitions for auf wiedersehen that I've seen before include "see you" , "Wanting to say farewell" , "so long in parts of Europe" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.