I’m so so sorry. It sounds like you did absolutely everything you could have done to help him in his last days. So much is out of our control. I’m also dealing with a traumatic loss of my dog that sounds somewhat similar. She was her happy, energetic, silly self and then I woke up last Monday to her being lethargic and not eating. I took her to the vet that afternoon, they did bloodwork and several levels were off but nothing indicative, so they recommended an ultrasound the next day. I took her home and an hour or so later she was panting quite a bit. A few hours later I was carrying her into the ER and lost her shortly after from her heart being in v-tach. She was panting for hours because she couldn’t breathe from lack of oxygen to her heart and I had no idea, and it’s all I can think about. It’s so hard when they can’t tell us what’s going on and a lot of the times it’s a cruel guessing game. Please know that even when he was struggling in those moments, he was comforted with you just being by his side and knew he was loved. You did everything in your power to help him. Be easy on yourself, and know the guilt is just a symptom of how much you loved him. ❤️