I believe as you grow older, the lines do blur, not only regarding “girls” but in general. When you’re younger, your parents explain the concept of “good” and “bad” in very basic ways. “Stealing is bad.” “Killing is bad.” These examples don’t include exceptions because kids won’t be able to grasp them.
As you grow older, learn more about the world around you, you find that “stealing” is not so bad when you are living in poverty and have to feed your family. That “killing” can be justified as capital punishment.
Also, what constitutes “good” and “bad” differs from culture to culture. It’s an interesting question.