Learn Portuguese (Portugal): Com quem vives?

In English, we often put the preposition at the end of a question, like in "Who do you live with?". In Portuguese, you cannot leave a preposition at the end of a sentence. It must always come right before the question word it belongs to, acting like "With whom do you live?".

Why isn't there a word for "you" in this sentence?

In Portuguese, the verb ending usually tells you exactly who the subject is. The -es ending in vives only belongs to tu, which is the informal "you". Because the subject is already obvious from the verb, the word tu is usually left out to sound more natural.

How would I ask this same question formally to someone I do not know well?

To be formal, you need to use the você form of the verb. You would drop the "s" at the end of the verb and ask Com quem vive? instead.

Could I add é que to this question?

Yes, you can! You could say Com quem é que vives?. Portuguese speakers often add the phrase é que immediately after the question word to help frame the sentence as a question, but both versions mean exactly the same thing and are widely used.