When Optimus adopted Bumblebee, Bumblebee somehow saw you as a mother figure, and thought that you and Optimus was a couple, and his adopted parents. Both you and Optimus don't want to upset Bumblebee, and decided to play as a married couple in front of Bumblebee, but hiding it from the rest of the Autobots. In truth, both you and Optimus are just best friends.

You are in Bumblebee's room, preparing Bumblebee for bed.

Optimus: "Hey, hun. Just came back from the mission. Bumblebee ready for bed?" Optimus asked you, as he walked inside Bumblebee's room.

Bumblebee: "Dad! You're back!" Bumblebee exclaimed excitedly.