I am the same Chickens, I don't drive, so could only walk our boy when dh was around. Fortunately for us at the time, it was long before we had children, so we could both go out at the same time without needing a babysitter - I appreciate that might not be an option for you.
Don't feel you need to apologise for how you are feeling, I've been there and it's just horrible.
Our boy was reactive to people, unless he knew them from a pup, as well. If you took the time and trouble to introduce them to him properly once, he never forgot them, would love them forever and was the softest, sweetest boy - but he couldn't handle being approached by strangers. Unfortunately due to his size and general appearance - he looked like an enormous Ridgeback - not many people wanted to try and get to know him. Which of course I completely understood, but it broke my heart at the same time.
Keeping him had such a massive detrimental effect on our day to day life and social life that we did eventually reach the point of no return and sit down and discuss having him pts. We cried together for hours, we hugged each other and our boy and we came very close to making that decision, but in the end, one look from his beautiful big brown eyes was enough to give us the strength to carry on. It was a truly horrendous time. 
I used to fantasize about winning the lottery and buying a property with tonnes of land where he could run free and be relaxed and happy without bothering anyone else. (Still do that actually, even though I now have a great soppy lurcher who's friends with everyone.)
At the end of the day, just like you, he was our boy and we couldn't give up on him. It wasn't a decision we took lightly and we had to seriously consider him, us and the safety of other dogs and people. To be honest, it was one of the darkest periods of my life ... but we came through it.
Like you, we decided to get another pup. Having had the problems we had with our boy, we decided to go for a pedigree (the only time we ever bought rather than adopted) and that's when we got our Soft Coated Wheaten Terrier.
Having her was like a breath of fresh air. I walked them separately and with her could enjoy all the good things about walking with a dog. I took her to two dog clubs and she came to college with me to do Canine Studies. We did a bit of agility, obedience and even heelwork to music and surprisingly, once we leaned off trying to 'fix' our boy and my stress levels reduced through enjoying another dog he seemed to suddenly improve. Of course it could also have been something to do with, having managed to live with another dog, he was finally learning something about canine communication. He even decided my Dad's JRT was an acceptable friend and then Dad's neighbours 2 JRT bitches and we had some lovely times walking them all on the beach together (I love walking on beaches as it's so easy to scan for other people or dogs).
Looking back, it was having him that pushed me into learning properly about dogs and their behaviour. If it hadn't been for him, I would still be clueless and without a doubt, having him made me a better dog owner. He taught me the reality of what all the rescues say about a dog being a lifelong commitment and made me look at and think about the way I lived with my dogs and what I could/should change to do it better. I owe him such a lot - and so do all the dogs I've had since.
No-one can tell you what to do, it's such a hard situation that all you can do is ask yourself those really hard questions and be brutally honest with yourself about the answers. Not everyone is in the position I was to be able to manage and modify their dog's behaviour and what we did would not necessarily be the right choice for someone else.
I'm posting because I want you to know that I do know how you feel and you are not alone in this. You are a lovely person, who loves her dogs and wants the best for them - if you weren't this wouldn't be so hard, because you'd already have done what thousands of people do every day and give up on Jas without even trying.
I know it's easy to say, but try to be kinder to yourself. What you're going through is extremely stressful and isolating and you need to find other things to do and focus on so that your life doesn't end up completely revolving around Jas, as that wouldn't be good for either of you.
The only thing I will say is that if the behaviourist/training sessions don't work out - do give the Dog Communication people a call. I have no experience of them myself, but have been on threads on other dog forums with some really experienced people who rate them extremely highly. I really wish they'd been around when I had my boy
I don't have all the answers, but I do understand - so in the absence of being able to fix it all for you I am sending you some very unMNetty ((hugs)), a pack of tissues and a strong
.