The past perfect tense needs a past reference to refer to the time before the reference. In your sentence, the reference point is the separation, and the playing together happened before that point. The first problem is that you've tried to establish that reference point with the past perfect tense ("had gotten separated"), which of course, wants its own past reference point, and English syntax isn't up to the job.
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samuraibabesIs it OK if I say : "We had always been playing together until we had gotten separated"No. Actually, it's rather difficult to assign meaning to your sentence. The word 'always' seems out of place.
samuraibabesWould it be weird if I saidNo. You can do that, though I can't guarantee it works for all verbs. What would be weird (or maybe I should say somewhat rare) is finding a situation in the real world where you would need to say such a thing.it"I'd liked eating cakes" ?