Ryan, the issue I have is that your narrow idea of "right" is what's limiting your ability to accept other valid ways.  This is not a case of Jesus telling us that premarital sex is wrong or that marriage is the only option for everyone. We need to accept that there are a great many good choices that people can make that don't fit into the "right" things you've mentioned here.  After all, it's not your duty to judge other people's decisions, but to support them in their times of need and to love them as yourself.

Because, as you said on your own site, "I don't want to say here that everything is neither right nor wrong, or that it doesn't matter what you choose in life.
But 99% of the time: It doesn't matter."  

These minutiae of premarital sex, cohabitation, and age are, in the greater scheme of things, not all that important.  What does matter is the relationship between the people, and that cannot be measured by any simple metric.  Love, understanding, and compassion for one another <i>does</i> matter.  Communication matters.  Age, sex, and residency can't create or destroy those things.