The Forgotten Ones by Andrea Bills

Caitlin and Dean grew up in the same small town and where high school sweethearts. Dean ends up leaving unexpectedly and doesn't explain to Caitlin what was up. When they meet again they are both looking for a killer in their hometown that seems to be targeting Caitlin. She is now a FBI agent and she has not idea the power Dean has with his military job. As they work together to catch the killer neither of them can deny the feelings they have for each other, but there is a lot of truths they both need to face before they can move on together.