Is before we went out a main clause?

No, "before we went out" is not a main clause. It is a subordinate clause that functions as an adverbial clause indicating time. A main clause, also known as an independent clause, can stand alone as a complete sentence and typically contains a subject and a predicate. In this case, "before we went out" does not express a complete thought on its own and is dependent on the rest of the sentence for clarity.