He's not a believer, but is he a decent person? ie not doing wrong things in your house? That could be a point to make with him should the subject of right and wrong come up. Though God is the one that initiates a person's understanding of their need for a Savior, you can lead by example. Make the difference obvious, and when the subject of standards comes up he will either listen to your personally expressed point of view or he will leave with a retained recognition that God must be the one in control.