Basically, the question seems to be how exactly single Christians should relate to members of the opposite sex in that large and awkward zone between "we've never met" and a deliberate dating or courting relationship. I won't repeat the full history lesson here, as several Boundless authors have already discussed it (Joshua Rogers most recently, in his excellent piece "Your Friendgirl Deserves Better").
Essentially, the historical reality is that until 30 or 40 years ago, long, intimate friendships between men and women in which each served as the other's emotional confidante, relationship adviser and "best buddy" were far less common than they are today.
As I've discussed before, a broad (but sound) implication of this passage is that "defrauding" could include inappropriate emotional — as well as physical — intimacy.Romans 13:8-14 calls us to love others, to work for their souls' good rather than looking to please ourselves.More specifically, verse 10 reminds us that "[l]ove does no harm to its neighbor." Romans 14:1-15:7 offers a discourse on favoring weaker brothers and sisters above ourselves, valuing and encouraging that which is good in the souls of others.Let's assume for the sake of argument that your intimate friendship is one of those rare jewels that is devoid of the potential for hurt or confusion. In the past, when both sexual immorality and intimate male-female friendships were much less accepted and less common in society, men and women moved more deliberately toward marriage earlier in life.By offering a taste of the companionship and interactions that make marriage so satisfying, with none of the accompanying commitments or responsibilities entailed in marriage, intimate friendships discourage the pursuit of the grown-up, God-intended outlet for marital desires — marriage.