Gabby didn't work under him on truck when they got married. She was back to being a paramedic. If Matt is Battalion Chief, it's an entirely different conflict, as now EVERYONE: Truck, Squad, Engine, Ambo, works under him. So him choosing to be boyfriend first, over chief of the house, would have a much different impact.
And yes, there were times, when he lost all focus over Gabby. The day he made captain, and Gabby was stuck in that parking lot, he was willing to run in, with no gear and despite the fact truck mates were fully prepared to go in, just because it was Gabby who was trapped.