Alone
In all his years of being alone, he was never as alone as he was now. Threw the many year of his life, he had met people, loved people and lost those people. It was a never ending cycle of meeting them, loving them and watching as they died. Knowing there was nothing he could do to help or to stop it from happening. The only thing he could do was live on and remember them, which was all he could ever give them. The promise of being remembered.
He had never in all his 150 years of life, loved anyone as much as he loved Ianto. He had never loved any team more than he loved this one. They were all some of the most amazing, infuriating, and the best people he had ever met. Owen, Gwen, Tosh and Ianto were his team. Now they were all dead, and it's his fault. All of the people he loved and trusted with everything he is, are dead. Ianto, his lover the only person who new him completely was gone never to return he would never hold him in his arms again. In a manner of months he had lost all his team except Gwen, but eventually Gwen would die just like everyone else.