It isn't jealousy, not like the Doctor expects it.
Sometimes, he forgets who he is traveling with.
It's easy to simply consider him "the companion" and leave it at that. Especially after determining that he is, in fact, not the Doctor, just a Thing that looks like him but isn't.
Sometimes, the Doctor wanders past his room and hears him snoring through the door. It's a low rumble, the vibration of respiratory structures the Doctor doesn't have, signaling very deep sleep. He wonders if the Thing dreams.
The Doctor can't think of a time he slept like that. So soundly. A Time Lord only needs a few hours a week. For the Doctor, they're generally collected when, like a wind-up-toy all out of spin, he drops unceremoniously onto his bed for a few hours of dreamless trance. It's not the same as sleeping. There's no ceremony to waking from a trace. No restfulness, no morning tea needed to jolt the system.
He often sees the Thing with a cup of coffee in the morning. He says he "needs" it when they land somewhere earlier than his sleep schedule is prepared for. Dreadful stuff, coffee. Donna liked it. Black, a few sugars. The Doctor wonders if the Thing dreams about Donna.
He can't even remember Donna, not unless he really, truly wants to pull her memory from his mind and see her in front of his eyes. There's no simple nostalgia in a Time Lord psyche. No happiness in a quick memory, no fleeting thought about a past loved one. It's all or nothing. Complete, perfect memory with all the pain and anguish, or just the knowledge that at some point he traveled with someone named Donna. To some, the eidetic memory would seem like a blessing. To a Time Lord with 900 years of past pains sleeping inside of his mind, it hurts.
He's not sure when he fell asleep, fully clothed, on his bed. It was probably early in the morning, at some point after he repaired the fluid link and recoordinated the neutron flow. But he wakes up feeling no different than he did when he lay down, except for a blazing headache.
The headache might be from the terrible noise blaring from down the hall. A tinny, whiny crash of sound repeated over and over. There's no real pattern to the noise and the TARDIS doesn't feel like she's in danger, so he straightens his tie and follows the sound.
It is, surprisingly, coming from the Thing's room.
The door is open and the Doctor peeks in. The Thing has apparently been quite busy during the Doctor's sleep-trance. He has discovered an old pair of jeans and a t-shirt from the wardrobe room, and has apparently re-opened the attic and rummaged through some of the things the Doctor has abandoned there. Such as the red, shiny electric guitar and amp, both given to the Doctor many years prior by Prince. Or, at least, the guitar was given to the Doctor by Prince, he thinks the amp might've been given to him by Joe, the guitar collector in 1998 when he mentioned he needed an amp for the guitar Prince gave him.
The Doctor remembers being so thrilled when he received the guitar. He'd always wanted to learn how to play but never got around to picking one up. He found a book on how to play in one of Jo's old cabinets and sat down to learn a little bit. He managed to learn five chords before something attracted his attention and the guitar was put down and forgotten.
Now, the Thing has the guitar. He's throwing himself around the room, playing those five chords over and over with elaborate hand gestures and even sillier dance moves. He bounces off of his bed and spins around, lifting the neck of the guitar up with one of the chords. He's a rock star in miniature, imagining himself playing some amazing song and listening to the cheers of the audience. He's oblivious to the Doctor, leaning in his doorframe, lost in his own imagination.
The Doctor has never thought to lose himself in something so silly.
But it looks like so much fun.
Chord. Chord. Chord. Spin kick off the bed. Chord. Chord. The Thing makes some noise that the Doctor imagines is supposed to be a cheer, then turns around and freezes.
"Oh---" His hair is wild and askew, his face is flushed and sweaty, and he looks completely and utterly humiliated.
He looks so alive.
Dreaming, waking, imagining, feeling. These are things the Doctor can't have and the Thing has them. He has all of them coursing through his veins. Even as the Thing gingerly takes off the guitar and flips off the amp (with a loud pop) like a little boy caught playing with his Dad's things, he's still so much more than the Doctor.
How could the Doctor not envy that?
"I didn't think I'd wake you," the Thing says. "Thought you'd be unconscious---"
Out, not asleep. Thinking, not imagining. Alive, but not living.
The Thing continues to talk, but the Doctor turns away from the room. He puts on a pot of tea and tries to imagine what it would be like if he really needed it first thing in the morning.
He doesn't have the imagination of a human.
He wonders if his companion knows how much he has to envy.
Muse: The Doctor (Ten)
Fandom: Doctor Who
Word Count: 912
Special thanks to handysparehand!