Though not a Biblical doctrine or salvation issue, we as the leaders of our church decided to expect our members to only date committed Christians. A woman who was part of our church some years ago returned recently, and she brought her boyfriend with her. She studied the Bible with some women in the church, and her boyfriend studied with some of our men. She finished her studies and was restored to our fellowship, but he stopped studying and has not made the decision to live as a disciple of Christ, and they broke up. Some time later, she resumed their dating relationship, against the direction/advice of our leadership.
     Our decision was to let her know that, while she could continue to attend, she would no longer be considered a member, and that this would be conveyed to the appropriate ministries. Some members thought our decision was unfair. Some questioned our biblical basis. I know some scriptures about church discipline (Mt 18:15-20, 1 Cor 5, Titus 3:10-11, and especially 2 Timothy 3:14-15), but, I believe these (and other) passages about church discipline are not directives to follow but examples to be examined and applied according to the different situations we encounter in the church.
Can you help us with some insights?

As you say, each leadership group must make its own decisions. I guess I feel about someone who is infatuated with a non-Christian the same as I feel about a brother who is grossly overweight and a glutton; someone who spends all his time watching TV; or someone who never has personal devotional times. In a sense, they all need discipline; but what is the best approach in each situation?

Since the matter is never directly addressed biblically, we need a lot of wisdom. I assume you read my 2004 paper on Dating & Marriage (Tokyo). I don't think my opinion has changed much since then.

Be careful not to add rules to God's Word. On the other hand, you do have a pastoral responsibility to protect the flock. Pray for wisdom (James 1:5), consult with seasoned spiritual leaders (Heb 13:17; Proverbs 13:14, 15:12, 19:20), and trust God to work through the process (Rom 8:28).