Sorry to hear about your boy. I hope you can find someone to walk him, but bullies do not require a lot of exercise and if it makes him nervous, then I would not do it. Plus I would not take him to doggie day care. That will only make him more nervous or stressed. Dogs who have been through this like he has, are sometimes happy just being by themselves and their human family. I would just give him time, some peace and quiet, and hopefully in a few years he will settle down and maybe one day will trust other dogs, but I would not push it.