Put down my 16 year old dog.

He was a miniature dachshund. He was my Grandma's dog, and she wanted me to take care of him when she passed. I had this dog for 1 year and 9 months. He loved her, and over time he came to love me too. His condition degraded over the past few days. It was very hard to feed him, I had to shovel food into his mouth, but I had to be careful because it was hurting. He had a red tumor on his side that started bleeding slowly. It wasn't there a few days ago, it rapidly appeared. I think it was Hemangiosarcoma. He was having trouble standing up at his water bowl; I had to lift him up so he could finish drinking. And when I took him outside to use the bathroom he would lay down his front and back on the grass. It was hard to get him settled down and sleeping as he usually does, and he seemed to be in pain. His name was Shadow, and he was euthanized in my arms at the vet. I was surprised by how fast the process was. I ended up crying as soon as the needle injection started, even though I didn't think I would. And now I feel empty, not needing to take care of him; he was rather high maintenance.