Have had several cats get it over the years. Knew a dog that had it and went through chemo - poor thing couldn't hold down her food and died about 6 months later having gone through chemo the entire time. The owner said she felt so bad about doing the chemo because the dog never felt good due to the chemo so the "extra time" never really mattered for the dog.
Some dogs can go into remission with chemo, but chemo doesn't guarantee that the dog will go into remission. Those who regret the decision of chemo the most are those who chose it because they "couldn't bear to lose their pet" and would do anything to keep it alive. They realized afterwards that their decision was based on their own selfish reasons and not on what was right for the animal.
Don't second guess your decision. You based it on the dog's needs not your own comfort. And that makes it the right decision - regardless of which way you take.