They're probably all going to have it if one of them does. Small town, insular little group of people who probably aren't too popular there? Yeah, within a couple years of joining that group most of them will have gone out with most of the rest of them at least a few times and they'll have swapped all of their diseases and infections around.
Worse, none of them are really well-educated and fewer still seem particularly sophisticated about biology and sexuality. They may not have the faintest idea what cold sores are, how to care for an outbreak, what precautions to take, or what happens if precautions aren't taken. I've met bright college kids who didn't know about that, and these women are nowhere near their level. If just one of them fails to do everything right, they'll all get it within a year or two.
Just in case you needed to have more awful images to sing you to sleep tonight!