Did your vet mention surgery or at least speaking to an orthopedic specialist? An ACL tear isn't going to ever heal itself. Scar tissue may build up in there, but the ACL doesn't repair. Once it's torn, it's torn.
If this were my dog, I'd stop throwing supplements at him and go talk to a specialist to get a real game plan. Living with one torn acl has to be painful and hard, I couldn't imagine having to go through the rest of my life with both of them torn.