But what about love and loyalty when no one else seems to be hurt, such as premarital sexual relationships? Such an argument does not apprehend biblical love. Love is not simply the absence of obvious injury to anyone. For example, critical thoughts don’t victimize, but they are unloving and wrong. Defining love in terms of whether people get hurt misses the heart of biblical teaching. We may not automatically decide what form love takes. God tells us how to love. When we love on our terms rather than His, we are in sin. Even if our sin does not seem to hurt another human being, it is still sin. If sin were reduced to hurting others, then we could become morally perfect by isolating ourselves from all people. Sin, however, is not primarily a human-against-human action. It is human-against-God. God defines love as obedience to Him.
Edward Welch