Haunted Souls - Kathryn Knight

Four years ago, Emily Shea and Staff Sergeant Brett Leeds agreed to part with no strings attached. Sparks flew during their brief affair, but fate intervened, sending Brett overseas. When an unexpected pregnancy derailed Emily's own plans, her attempts to locate Brett were soon overwhelmed by the challenges of single motherhood. Now, Brett has returned home, and Emily is forced to share her secret. 
Despite feeling betrayed, Brett is determined to forge a relationship with their son, Tyler. As the former lovers battle both their inner demons and their mutual desire, another presence enters their lives—Tyler's imaginary friend.