What else can I say to my friend about his relationship?

I have a friend (we are both adults) that is in a new relationship. He claims to be a Christian but the woman he is dating is not. I talked to him yesterday about it, and mentioned that scripture tells us (that are Christians) not to be unequally yolked with unbelievers. 2 Corinthians 6:14. I didn't go into great length of discussion but I said his relationship is not God honoring and that he should share Christ with her. He said he has talked to about Christ once but that was it. He doesn't seem to care that she isn't a Christian. Basically the two cannot properly please God because she is not a part of the family of God. So they cannot glorify God in their relationship. I am also led to believe he has fallen away from the faith, which is part of why he is making this compromise. I also think he doesn't want to be alone so he is settling for what he can get. Thoughts? This is for Christians, not anyone here to bash or talk about religion.