תרגום - איטלקית-אנגלית - Erano mesi che non riuscivamo a passare un fine...

Eppure in classe è stato tradotto "It had been for months..." and I don't know the explanation

You are right. I've confused "erano" with "ci erano".

I translated like this: It had been for months since we couldn't spend a (single) weekend in peace.

or "...we couldn't manage to spend..."