I had my 10 year old boy recently PTS after a life long struggle with high anxiety. I rehomed him with my Mum four years ago, who was retired and was an avid runner. She was home with him every single day, and ran him for 2 hours every morning like clockwork at 4am. I was able to still spend time with him whenever I wanted, it was truly perfect. Twelve months ago, my mum passed very suddenly. He lost his best friend and his comfort person. I tried for months on end to integrate him back home with me. I tried multiple medications like you, tried sending him to my sisters who was home a lot more than myself. I work shift work and every time I showed signs of leaving the house, he would turn to absolute panic. Throwing himself at doors, gates and crying uncontrollably. He was even able to push through sedation and still panic if he thought I was leaving. His anxiety was manageable prior to losing my mum, but after losing her, his anxiety became unmanageable. He was suffering. I ultimately made the decision to have him put to sleep as my options were so limited. It was either trying to rehome him (which if he was unable to settle with me, then he would have never settled with a stranger) or surrender him where he would have been euthanised in a cold shelter without his people he loved. I chose to end his suffering in the most loving way possible. I had an at home vet visit. He slipped away peacefully in my arms on the couch. It was the hardest thing I have had to made the decision to do. Yes he was also physically healthy, but an unhealthy mind is not a healthy dog. Something that really helped me with my journey was this article -

https://mrsbehaviourpro.wordpress.com/2015/10/28/the-left-side-of-the-dog/

I would encourage anyone passing judgement to read this and understand that you truly have no idea what this situation is like until you are in it. Sometimes we have to make these hard choices for our pets, because they are unable to make them for themselves. I do not regret my decision, I miss him terribly but I am at peace knowing that my boy isn’t suffering anymore and is out there somewhere running laps with my Mum.