You would never know with the way he smiled and laughed around Rose, or kissed rose, or even joked with the ponds, but the doctor was a very sad man in a box. He was sad because he knew that no matter how much he loved someone he could never stay with them, because they would age, unlike him, a timelord. Timelords never aged, they regenerated. But they would never really die. This is what made it so hard for the doctor, He always knew he had to leave, so trying not to get attached was his priority, but he had a hard time with it. He knew at some point he would have to leave, he couldn't stand to see them age and die when he knew he couldn't grow old with them. He also knew he didn't want to leave them. But he had to, and he hated trying to explain it to them either. Because it would hurt. So he would either go back in time and change it, or leave when they wouldn't notice, it broke both his hearts. But he had to do it. So to this day the doctor does what he's always done. He goes around all of time and space finding people he loves but can never be with for a long time because he knows it will always end the same, A sad man in a blue bow with two hearts broken.