A lack of stability over something as important as ‘where will I live’ can have a massive impact on your mental health. It sounds like, with your son possibly moving out your housing situation may not be the only change on the horizon.
First things first, let’s get your housing situation sorted. Different housing providers have different ways of dealing with flexible tenancies so it is important that you talk to your housing provider about how they will proceed. You can ask for a copy of their policy and this will enable you to prepare for what may or may not happen.
Shelter is an excellent website providing advice on all things housing and is most definitely worth a look. Your local Citizen’s Advice Bureau can also help to give advice on your housing situation however the wait for CAB advice around the country differs dramatically.