Devil and the Deep by Julie Ann Walker
A former Navy SEAL had rescued Maddy once before, and they developed a relationship. Through his own stubbornness, he tried to forget her and move on with his life. Unfortunately, a sunken treasure ship is a goal for a few. Too bad someone wants to kidnap Maddie.
Navy SEAL Bran to the resuce. Without his knowing who, he finds Maddie in the same situation again, in need of rescue.
While the story starts out about a treasure hunt, the majority seems to gear towards their relationship and the past, and what type of relationship may or may not happen now and in the future.
Well written and easy to follow with quite the cast of characters, there is something for everyone.