Sorry to hear you are still struggling with your boy.
If his anxiety is increasing and he's generalising it to you even leaving the room it might be time to have a chat with your vet about pharmaceutical treatments. There are specific drugs they can try to reduce anxiety while you do a Separation Anxiety programme.
Don't Leave Me, by Nicole Wilde is an excellent book for helping you to work out what type of SA he has, what his triggers are and what to do about trying to help him.
As for the recall, recall issues aren't unusual in dogs with Lurcher/sighthound of some sort in them and he has Pointer as well - so a double whammy really. I would invest in a longline and keep him on that, until you feel he's reliable enough to let off, as it really reduces the stress around worrying if he's going to come back or not. You don't need to hold the line, just let it trail and then you can stand on it from 30ft away if necessary if he decides to do a bunk.
Having said all that, if you are really struggling and the rescue centre is in agreement that he needs a completely different environment, having had dogs with SA myself, I can understand you feeling he might need a different home. Sadly the sort of home where dogs can have the freedom to run around a large outdoor area and have someone home all day are few and far between, which is why so many dogs with these issues end up in rescue for prolonged periods.
I do totally understand how you feel though. I adore my pup and wouldn't part with him for the world, but I have had days where I have been in tears because of the restrictions he's placed on my life and freedom and at one point did actually say to my dh that much as I love the pup I sometimes wish we'd never rescued him. I feel terrible for even thinking it and as I said, would never part with him, but some days it just really gets on top of you and you can't help how you feel.
I console myself with the fact that he is still so young and I know from past experience he will settle down a lot when he reaches maturity. This adolescent stage is the worst when you have a dog with any issues, but it does pass eventually. The girl we lost last spring was a nightmare from pup through adolescence. She was by far the most difficult dog I've ever had, but turned out to be an awesome family pet once she matured. I have stood on the edge of a flood plain for over an hour while she and another adolescent taunted myself and the other owner just out of reach and up to their elbows in stinky water, spent over a year working on getting her walking on a loose lead, even longer training a reliable recall, dealt with the SA she developed when we moved house and despaired of her constant barking, but she turned out to be the dog that I would trust the most out of all the dogs I've ever had and I miss her sooo much. If you'd told me 14 years ago I'd have felt like that about her, I'd have said you were barking!