Hugs to you! I think it's the right thing to do. Animals try to act like nothing is wrong, like being in pain, when really they are hurting. My black lab was extremely hurting from liver failure. I didn't even know it until it was too late. I took him to the vet, he was skin and bones from not eating or drinking for 4 days. He was hooked up to iv's but still wagging his tail when he saw me. But he had this look in his eyes that I knew he was ready to go home. It was the hardest thing for me to do because I felt like you, like I was taking his life. Just know that you are doing the right thing.
If you ever need to talk I'm here for you. I'm sure everyone else on this board is here for you too!

Hope your doing ok!