Optimus was your Guardian. He never thought he would have to take care of a human who had no parents (your parents were killed by the decepticons), but here he was. He would have chosen Ratchet, but of course Ratchet denied the responsibility of taking care of a human.

As the human, you have grown used to the fact that Optimus wasn't always there to spend time or have fun. He's in war for crying out loud, he's got a whole team to lead. He's trying not to get attached to you, it was better than getting drawn away from war....but you mean the world to him....Taking a ride in his semi truck alt mode was always peaceful after a hard day of school, that was the only time you got to spend that small amount of time with him. His emotions were a little intimidating to you at first, considering...well-...he rarely showed ANY emotion. But you've got to learn that underneath a stoic facade was a shy and gentle fatherly mech trying to hold everything together.

Currently it was just you, Optimus and Ratchet in the base alone while Bumblebee, Arcee, and Bulkhead were out and about with their human allies, Raf, Jack, and Miko.