It must be very hard for you to be in this situation but you have had many years of bringing him up, and you deserve to live out the rest of your life and have some time to yourself. You already know it is not going to work and you are feeling under pressure, it will end up with a big fight and you having nowhere to live, so my advice is do not allow him to move back in. Also if he had regard for you he would not put you under this pressure, he is old enough to look after himself. We all have difficulties in our life but I do not think you are doing him any favours anyway, by letting him move back. You are being bullied into it already and it will all end in tears, so better to be tough now even though it is not easy it is the right thing to do.