i am glad he is better! I am sure you did right way before. No matter how right you will do our pets can get sick just like we are. I have one betta that is older than 5 years old. And the other betta that i bought the same time died about 2.5 years ago. So never blame yourself. You rescued live creature and give him life and love and its all that matter. We try our best to help them. Do you need any advice on water changes or anything else?