Blackfellpony living with a reactive dog is hard - I know i have one! I too long to have a "normal" dog. My guy is dog reactive but to any dog even a dog miles away. He is now 6 and we can manage most situations - he trusts me and I am aware of what he is capable of and what he can deal with.
I have worked with him and we can compete in agility - but could not walk past a dog in the street without him going ballistic. We have to drive to far off places to walk him to avoid others.
However reading your thread your dog can do loads - the ability to walk him in group walks, and him being so loving and calm at home is an amazing step for a young reactive dog - you must have worked so hard with him.
It can feel very isolating, feeling like you are the only person in the world with a reactive dog and also I know the feeling that you think people are judging you and blame you. Intelligent knowing dog owners will recognise what a fantastic job you are doing.
I run a naughty but nice dog class and see every week how hard the owners of reactive dogs work. Some people are lucky and get dogs that do not need loads of training. Reactive dog owners put in hours and hours of training, they rearrange their lives for the dogs - they all should be recognised for being the awesome owners that they all are.
Your dog may continue to improve but there will always be occasions that will trigger him and to help you be able to live with that you need strategies in place.
You are correct to always use a muzzle and a double ended lead attached to a head collar and a harness.
Waits to be shot down in flames here but a reactive dog dos not need a walk outside every day - they do need stimulation and exercise but this can be done in the garden of the house - if interested I can give you games etc to help with this.
By not walking everyday you can bring down your dogs stress levels (and yours!) and relax and enjoy your dog and what he is good at.
When we go away we get a dog sitter to come to our house - they are under strict instructions not to take the dog off the premises. It is ok for the dog to live within their limitations for a while - after all the alternative is to be cooped up in a boarding kennels for a week!
I also understand you thoughts on PTS and you would not get a flaming from me if that is what you decide - it is a heartbreaking position to be put in.
Do get back to your behaviourist and also the person who runs your group walk - you need support. If I can help at all do pm me as I have colleagues all over the uk who could help you.
and
for you. Do not judge yourself you are not to blame for the situation you are in . You are a caring loving diligent owner who is dealing with a hard situation.