Could a Demon live it's life out inside of you?

Short answer is yes

Demons can occupy people,so much that they take over their person,and believe me when I say that they are evil in ways you can not see,even if it was right front of you.

On the other hand born again Christians having faith in the Lord Jesus Christ, can not be possessed by demons,for the simple fact that they're possessed by the Holy Spirit.

So ask yourself,who do I want to be possessed by: God Almighty, or Satan?

Faith