I too and withdrawing, by choice. And I feel real content with it ! Do you enjoy reading ?

CBT has some real science behind it- that the way you act incidences the way you think, not just the other way around. Doing the things you want to do, may force your brain to change. Start small and see if it works.

I can relate to the getting tired of being alone. Why are you terrified with going out? What do you mean you feel like you have nothing to contribute?

You are not alone, there are a lot of people here , who will value your input. And if things get really bad message some of those near you and meet up. Most of all if you are isolated think about travel, there is a whole world out there, and we live in the first age when travel is really easy, and you can meet people. And if none of that works do not be afraid to see you doctor mental health is a real need, and there is nothing to be ashamed of in seeking help to attain it. If you are retired, think about charity work to give your life purpose, there are lots of charities who need all the help they can get.