> protect him from the dangers he doesn't yet know exist or may not yet understand

This is the big one for me. My job is not primarily to protect my children, it's to prepare them to be functioning adults. To that end, I protect them from dangers that they're not yet ready to face, while teaching them skills to recognize and handle the dangers eventually.

Have you discussed pornography with your stepson? If you haven't seen it already, https://fightthenewdrug.org/ is a good resource.