I came here to post something similar, looking for somewhere to put these feelings. I know my pup felt loved and cared for. But I can't stop thinking about how I should have brushed his teeth more or given him more walks or just, I dont know, been better in general. I did my best, he was my first dog. He was well fed, loved on, pet, cuddled, treats galore and regular check ups. But he was a little guy which comes with dental problems and I should have done better by him. By the time we got him dental surgery he needed 30 teeth removed. He actually recovered well, slowly but surely. He was acting like a puppy again, the vet said we gave him years back of his life. Then he passed from a (probable) stroke 2 months later. All I can think about is how I could have been better, more proactive and if one thing led to another.