Devotion takes a few forms in Trajectory.
First off, there is the devotion between Joe and Claudette. Despite the giant impasse of children, the two are incredibly devoted to each other. Claudette continues to take care of Gertrude while Joe is away. Joe's heart is completely devoted to her, even with the introduction of Michael.
There's also Joe's devotion to his work. Joe is a cop, through and through. It's all he knows how to do, how to be, and how to live. His off-time is spent training and shooting, and simply improving himself and his skills as a member of the SWAT team. Joe does nothing half-heartedly, and that very much shows in his devotion to his work.
On the flip side of that is his team's devotion to him. The SWAT team is very close. By nature, they must work as one unit. Communication is imperative, trust is a requirement. They rely on him as much as he relies on them. They are devoted to him, as he is the eyes that keeps them safe. Every member of the SWAT team respects and highly regards him. This is one team that is truly devoted to one another.
You could even say there is some devotion between Michael and Joe. Though their relationship is a most unusual one, they both look out for each other. There is a sense of devotion, albeit a strained one.
So devotion is a strong theme in Trajectory. It takes on many forms, and it very much encompasses the various relationships on Joe's life. D is for devotion.