It doesn't sound to me, that you have failed your son in anyway. As you say, you'very done everything you can to help him, it sounds exhausting. Maybe a long term placement will help all of you. I remind myself of the emergency talks they give on airplanes, that if the oxygen masks come down, it is yours that you must put on first. If you are trying to meet the complex needs of your son 24/7, how can you even start to look after your own needs? Being in placement, doesn't mean you stop being his mum, it just means that he can get intensive specialist care and you can look after your well-being, so that when you do spend time together, you may both enjoy that time better.