Sorry to hear about your current struggle LS. Single Introvert here as well. I find for myself that getting out and doing things that are vague interests can grow into something that will motivate you more later on. Finding a passion is hard if there is nothing to motivate you, but if you don't try a few different things it's hard to figure out what it is you may like.
Its like the saying 'how do you know what's your favourite icecream flavour if you haven't tried them all at least once?'
I don't do it often enough but I find going once a month to play boardgames or groups who go watch movies or just meeting up for a walk/ride around a local park or beach or amateur tennis groups is a good way to start your search. Then you never know , you might meet someone interesting along the way.
Maybe if your focus is meeting someone use that as your motivation. you can discuss with your shrink what it is you want out of a relationship and what type of person it is you wish to be with? From that, imagine what that ideal person has for hobbies. Using this formula might give you ideas about what hobbies to take up to happen upon that Mrs right.
Hope that helps spark some ideas.