I added a new page to the Hook Up Spanish Phrase Guide about asking and responding about who you live with. Examples:

Do you live by yourself?
¿Vives solo/a?
¿vee-vehs soh-loh/ah?

Who do you live with?
¿Con quién vives?
¿kohn kee-EHn vee-vehs?

I live alone.
Vivo solo/a.
vee-voh soh-loh/ah.

I have a room mate.
Comparto piso.
kohm-pahr-toh pee-soh.

More Spanish phrases discussing who you live with over here.