Either way, that person is now hanging on to the "friendship" in the hope of getting something more despite the "clear words" from the other person that he or she wants nothing beyond friendship.
In other words, they tend to involve much of the type of intimacy and companionship involved in — and meant for — marriage.
Bottom line: I believe it is difficult and rare — as a practical matter — to honor these principles in the context of a close, intimate friendship between two single Christians of the opposite sex.
(For the verbally precise among you, I think such friendships between non-single Christians are also a bad idea, but that's not what we're talking about here.) Intimate friendships between men and women almost always produce confusion and frustration for at least one of the parties involved.
As you probably know, I believe Scripture to teach that engaging in the types of emotional intimacy and companionship involved in close male-female friendships — outside of marriage and for their own sake — is wrong (see else I've ever written for Boundless).
But even if you don't accept that premise, such intimacy is still inadvisable in the sense that it delays and discourages marriage, which Scripture unambiguously calls good and right.