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It all starts with Rose Tyler. Nineteen year old too good for her ordinary life, too good for the Doctor.
Until she agrees to start traveling with him, of course.
Rose Tyler with idiot Mickey for a boyfriend and a loud mum living in the same flat they've owned since she was young.
The things she leaves behind for him. For adventure in a blue box that flings itself through time and space.
Love is inevitable.
But this time around, it's different. This isn't anything like the deep affection he feels for Sarah Jane, Ace or the others, and it's not the grandfatherly love he feels for Susan.
This is the kind that makes him want to grip her shoulders and press his lips to hers. To show her all the cosmos has to offer and more. That she is his stars, his sky, his universe. That he is Rose Tyler's and Rose Tyler is his.
His Rose Tyler who makes his hearts beat faster with a word and stops them with a smile.
His Rose Tyler who is gone too soon, sucked into the Void and into a parallel universe.
He breaks a little.
Which is when he meets Martha Jones. Martha Jones the medical student with an extensive knowledge of Harry Potter and the human anatomy.
She falls for the stars, the sky, and ultimately for him.
He pretends not to notice.
Because accepting that Rose is gone is something he refuses to do.
That doesn't mean that he doesn't love Martha.
He loves her in the way of close friends that are near and dear to his hearts, but in a strictly platonic manner.
She needs commitment, something he can't give her.
He knows its selfish of him to keep her around. He gives her false hope, indirectly bribes her into staying with him because he needs her company. Their relationship becomes toxic.
So Martha Jones leaves.
And he breaks a little more.
This leads to his second encounter with Donna Noble.
As far as first impressions go, Donna is bossy, rude, and takes to yelling at the Doctor whenever presented the opportunity.
Donna Noble with the temping career and failed marriage becomes the Doctor's best mate.
This is the equally shared affection the Doctor has always needed. The kind where he shows her the stars and she accompanies him through the galaxies they travel.
He loves her as a friend, and Donna the same.
Until she forgets everything about him and their travels. Saving planets and touring all of time and space is a lost memory.
The Doctor doesn't exist to Donna Noble anymore.
He is broken.
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Sometimes they're taken away. Other times they choose to leave, or he is forgotten.
No matter how any of them leave, he is always hurt one way or the other.
He always ends up alone.