Toughest decision to make but I agree with others, think about the dog rather than yourself. We had to put down a dog and a cat between November 2013 and February 2014. I was devastated about the dog but my daughter took it harder because she loved them both.
It took me over a year to say yes to my wife and daughter about adopting another dog which we did this past weekend.
My thoughts are with you. Our pets are a part of the family.