What is meant by not being enslaved to a non-Christian?

Question:

I'm confused about this verse about being enslaved to a non-Christian. Does not being enslaved mean you are no longer bond by the covenant of marriage or what? I've never study this verse and we'll be going to be hitting the topic of marriage again soon, so do you have any advice on this verse?

But if the unbelieving partner separates, let it be so. In such cases the brother or sister is not enslaved. God has called you to peace. (I Corinthians 7:15)