How can I make my dog's death less painful?

My family has owned dogs for my entire life (I bought one for myself three years ago). However, my first dog, the one my family got for me when I was young, has just formed a severe and rapid case of cancer, and is dying. Unfortunately, my parents - who have mostly raised them - have important family obligations they cannot skip. So, they brought him to stay with me. I think it's really sweet that they thought it would be best for "my dog" to spend his last few weeks with me, but I'm having a really hard time with it. I've loved this dog for almost half of my life. Do you have any advice as to how I can get through this?