Context of story?

so someone ask me :
what do you call a long-time customer, a long friend etc.

I replied :
What is the context of the story?

Person replied :
The context doesn't matter.
You dun need to know

and then.. :
Nevermind....

hmm... that wasn't very nice, wasn't it? It was a simple question....
The "you dun need to know" isn't really very nice...

Well, a long time customer could be called a loyal customer?
But it may not be the word you are looking for.
It could be that you are writing something about good-will?
Building up a good relationship with the said customer?
A long history in working together?
Based on past relationship?

Without the context of the story or email or whatever you are writing, it is difficult to come up with the correct word or terms which you can or should use.

Perhaps it would be better to "ask for help" when you are more ready to explain what you need.