It was generally assumed they would get married

English as a Second Language English Vocabulary, Grammar and Idioms
1

It was generally assumed they would get married as they had been inseparable since they were children.
What does “as” that I bold above suggest?

2

Hi it means" because" in this sentence

I think “being” could be true as well
But with being it’s better to say :
It was generally assumed they would get married being inseparable since they were children.
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3

Hi Clearsky, I think the most natural form of your rewrite would require a change of tense:

… having been inseparable since they were children.

4

In this context as simply implies a reason for the certainty of the marriage.