Well, we have a small problem here: the writers of the song are not actually native speakers, and have forgotten that "déjà vu" is actually uncountable to us English-speakers. We'd never write "a déjà vu" - it simply sounds wrong. You use "déjà vu" in the expressions "a feeling of déjà vu" or "a sense of déjà vu". If you dreamt about something and then saw it in real life the next day (ie. in Angelo's example), you'd say "it was déjà vu", "I had déjà vu", or just announce "Déjà vu!!"

As Angelo suggested this term is simply french for "already seen". On this basis your two examples don't really make sense. "I wanna live with you a "already seen" or "I'm leaving tonight, the last "already seen". I apologise for possibly being too literal but I hope you understand what I mean. It is better to use it as a noun - I had a déjà vu yesterday when I walked into the shop - I could have sworn I'd been there before. You can also use it in a more slang fashion "This situation is very déjà vu" - this suggests that you feel as if you are repeating yourself - like an argument you have with your mother or best/worst friend. I think the comment from Silver Fox goes some way to helping actually ........

Hello Maria, "deja vu" comes from the French language and is written as "déjà vu". It refers to a situation that you've been seen/met already before. It is indeed correct to say it to things or situations that you've already seen before (something familiar). Example: Last night I had a nightmare in bed about a car accident. The next day I went to town and saw a car accident that exactly has happened the same way like in my nightmare. So I can say: I have a déjà vu, because I have seen it already before (here in my nightmare). Best regards..

use it in my *speach*

I did But I really can't use it in my speaking that's why I try to get it completely to use it in my speaking. I wonder how could you remember that?