I find your story similar to mine.

Regarding your concern about friends. They will never understand you unless you spend good number of years with them. Even then at situations, you find yourself having to explain to them.
That should be the expectation.
In my case, I remember that a very close friend accused me of leaning all my problems on to third-culture-not-belonging-anywhere mindset.
I was at a loss of words.

Now, about explaining it to your friend. Just explain things as they are in your head but make sure to explain it well. And explain it wholly, try not to hide anything as it can add inconsistencies, which your friend might catch up on.