I learnt the hard way in some ways, first dog (Ben) when I was a kid got run over and after recovering picked up Hep B, so had a treatment oil or lotion or something as I remember it. I was too young to understand and went with the dickish 'slimey' outlook, so I didn't say goodbye and to this day I remember him looking at me sitting in his basket waiting for me to go over and cuddle (shortened version) I came back from school the next day and he wasn't there.
Not made that mistake again with either Giz (our cat after him) or Rox. Heart breaking both times but I had to say goodbye out of respect even though with Giz it was after the 'moment' as I was working and my folks + vet decided it was time. Funniest thing with Giz, couldn't stand Claire until she got pregnant and then became possessive lol Rox's shining glory was meeting my nan for the first time and if it hadn't been for us lot catching her, she'd have ended up on the floor.
I have a history of mental fucking animals.
As you say mate, every moment and whilst I hope both have years to come, you know yourself, be there for the final moment. It breaks you, but it's better than not being there.
I trust you've put both of them on this thread, for immortality!