Thank you VERY VERY much for your post. Please don't feel guilty, we all make mistakes with our furbabies and learn from them. By sharing your nightmare, you will help others from making this one.
I will keep you and little Andy in my thoughts and prayers.
Couplers can be a fantastic way to walk two dogs with one leash, however, each dog must be trained to walk nicely and then the two dogs need to learn to walk nicely and take their lead from you.