So, I absolutely agree, the question isn't "Where is the line", or at least it shouldn't be. The question comes down to "Why is there a line." The same thing comes in other areas as well... To use the analogy above, the commandment, "Thou shalt not commit murder" could just mean that you are not supposed to commit murder, but in the context of Deuteronomy, the command gains a lot more than that. It's not just that you shouldn't commit murder, but that you need to respect life. If your ox is in the habit of goring people, and you don't take care of the ox (that is, kill it), and it kills someone else, you have violated this commandment, and therefore are subject to the consequences. Jesus takes it further, loosely paraphrased, "If you have desired someone else to no longer exist, you have committed murder in your heart"

I think the sex before marriage has the same considerations. This all comes from the basic command, "Thou shalt not commit adultery," but can be stated in a positive way as well, "Honor the bounds of the marital committment."

Viewed that way, the question isn't about drawing a line, it's a heart issue. Is dry humping your gf/bf, is orgasm, etc. the question? No, the question is, what are you doing in that relationship to maintain the honor and sanctity of marriage. If you tell me that sex before marriage honors that committment, I will tell you that you are rationalizing completely out of bounds, because you've violated the foundation. If you can tell me, after searching your heart and truly allowing the HS to convict you, that dry humping honors the sanctity of marriage, I cannot convict you, but I really doubt that you have done the hard work. Much more reasonably, if you can say that physical touching (for the moment, let's argue outside of primary or secondary sexual features) is a way that you are honoring that commitment by being more capable of identifying what expresses love to you in the best way, I think that may be a reasonable statement.

Regardless, that's where we should focus on, not where's the line, or if there's a line, but why are we doing it... We do it to honor our spouse and honor God by respecting the institution of marriage that He founded in Genesis.  That changes the whole conversation.

As to the sex education, that's why I'm really glad that Song of Solomon is in the Bible. God does want us to enjoy sexuality and sex, but there are boundaries that make it more satisfying. Long-term monogomous relationships are the most sexually satisfying, but we don't hear about this in the church at large. We have become so scared that by talking about it, we will be heard to be endorsing sex anywhere at any time, that we don't talk about it, and thereby stigmatize it.