Caty I am so sorry for you and know the heartbreak you are feeling letting Ludo go. A few days after Ruby was pts we got a card from the vet, who had cared for her all her life. He wrote the kindest words and ones I would like to share with you now. He thanked me for ending her suffering and pain and said I had shown that I was as much of a friend to her, as she had been to me all these years.
It doesn't make it better or bring her back, but I know he is right and it was the right thing to do, just as you have done for Ludo. We can take away their pain even though it breaks our heart to do so.
Sending you lots of healing thoughts, run free at the bridge Ludo xx