Bible Verses Needed Regarding Abstinent Living Options

[Trying]

My friend (Christy) and her guy (Mike) have been dating for a while. We've all been going to church together, and he's a nice guy. They have not been sexually involved and are planning to wait until marriage. His roommate situation isn't great and she ask what I thought if he moved in. He stayed overnight with her before and I think their faith is really strong. I'm wondering what verse I can share with them, before they make their decision final. I can only find verses that say things like 'God's family should live together', and nothing saying 'do not live together'.

Any scripture-based advice (with chapter/verses) that I can pass along, would be great.

Thanks.


(P.S. =Their names aren't really Christy and Mike. So if you know a "Christy & Mike", it's NOT them! Don't approach them with advice.)