I don't think you should worry too much about "disapointing" Gus. With every living being, who has experienced hardship, there will be things that makes them worry if bad things will happen again. I think the main thing is to show him, that you come back again. And if he's upset, then try to make him feel better (give a treat/toy/cuddle etc), but if he is still upset, then let him be upset.
That is what I meant with PTSD. We are not always in control of what will prompt a negative response. I know Sugar will respond negatively to being to the vet, but I can't stop going to the vet. Same thing with you, you can't stop leaving the house/room every now and then.
I believe as with us, time will heal all wounds. Give him the time to figure out, that if you don't come back when he calls, then you will come back a little later. There is also a little intelligent creature, who might take advantage of your concern. The larger parrots are very clever and are indeed clever at making their humans do what they want
And to some point I do try to accommodate both Sugars and my wishes, but I cannot change my entire life to my PTSD feathered family member