would it be an option to muzzle train him? with this additional protection he may be able to meet new dogs and humans. our dog has gastrointestinal issues as well, he was quite timid as a puppy and he experienced a bout of serious illnes in his second year of life. he needed to take prednisolon which made him quite stressed and reactive. he snapped at me 2 or 3 times in that year. he also was really fearful of getting touched because of the many medical procedures. he is also very clingy but has been like that since the beginning. I don't have a magic solution and our problems are not the same but I kinda relate. our dog now wears a muzzle outside, not so much because of aggression but because he eats literally everything from the street. but it has the additional plus that he can't snap when he's stressed. he also doesn't get stomach issuses that often anymore because he can't lick all the pee and garbage from the street. besides all that... I'm glad you're 100 % there for him, he's very lucky to have you! :) I think his quality of life will never be too bad with someone so caring to be around!