Hi Hiding,True story, just about 12 months ago I first called in at a local session- it was one of the best things I have ever done in my life. Other than listening to music and maybe singing several months down the line - I had no expectations. All the session co-ordinators I know accept people passing-up a turn, or 'just' sitting listening/joining. Most performers I have come across LOVE to have others joining in on the choruses - so I doubt there's any time pressure on you. You can ake as much time as you like to build up a repertoire again - decide what what you WANT to sing and which venues feel most comfortable for you. I now sing/play guitar a couple of times a week - and in FRONT OF PEOPLE - not just in the car ! But also get to hear a wide range of music. I'm still a shy person - so to some extent it is still hard work, but from just gradually getting to know people I now have more friends now than at any other time of my life. Something that keep on surprising me is just how nervous MOST people are - you really won't be the only nervous person in any room. If you spot somebody there by themslves they may be particularly glad of someone chatting to them. - And with music there's always something to talk about !
Keep on keeping on Hiding, maybe reflect on each evening, & pick out a small peice of progress each time - perhaps you heard a song that you really want to sing, or you have learnt that a particular type of venue is/isn't for you, or a chat with somebody went particularly well.
When I was first starting singing at sessions - I found I could guage when I felt I was ready to sing a particuar song when I could sing it at work & not stop if somebody walked in the room.
...But whatever works for you Hiding
Good luck to you.