The Doctor wasn't known to be a open person or in this case, alien. Sure, he would talk all the time but he never really talked. He would go on about things but never share anything about himself. Except in random moments together he would tell his story. How his people were gone and not coming back and how he felt alone in the world for the longest time. He had lost his family, his people and you knew he would always hurt, always mourn them, for you saw the hurt in his eyes but you also saw how he was when he mentioned his Rose.
She could make him forget and you could see how much it hurt him to have lost her. You were his friend, you would travel and have adventures together. Across time and space. He would slowly reveal himself to you and break down his walls. You knew he was broken, from all the years he had lived and all the decisions he has had to make but you were a shoulder to lean on. Someone he could could count on in times of need. His best friend.
He told you parts of his story and slowly you could put together all the pieces. He was hurting and you were hurting for him too. Sometimes he would smile, a hint here and there but it would never last long. A second or two.
Then one day you saw him crying silently in the console room. Holding a picture in his hand, which you later would find out was a picture of the one he lost, and you knew for all the smiles and laughs that you could bring him he would always miss her and would never laugh or smile the same because she wasn't there.