Sorry for your loss 🙁 Loosing a pet is so very hard, and making the decision to let them go can make it even harder. The guilt for me was the hardest part to deal with since I lost my girl.
Just remember you gave him the best life, surrounded by love. And making this final decision was the ultimate act of kindness. (Thats what my vet told me, in a sympathy card she had sent me. It meant a lot, and helped me deal with the loss some)