Hi Lonesome Dove,
I can really relate to how you feel. I frequently felt invisible (and still do sometimes), like I am really quite low down on most people's priority lists. I think I am a nice person with many great qualities (and it has taken a lot of self esteem building to learn this), but when I feel like I don't have any proper friends and people to share my life with, I feel really isolated and sad. And I feel pathetic for feeling like that, but I am really very self conscious, shy and lacking in confidence.
I had counselling earlier this year and for me it was a bit like opening a can of worms. I was in two minds about continuing, but didn't partly because of the cost. It was like a bit of a crutch, but now I am no longer attending, if I have an issue I just try to work through it in my head like I would have done at counselling. Sometimes it helps. If you feel you still need to continue with the talking therapy, have you looked at lower cost options? Like the services some charities provide, and their fees are on a sliding scale based on salary? It might not be as good as the counsellor who worked well for you, but if talking helps you...
My issues really came to a head two or three years ago, when my self loathing was at its worst. What helped was, instead of dwelling on things when things went wrong (e.g. if a friend blew me out yet again, or if I wasn't invited to something), I tried really hard to turn the page and move on, rather than take notice of how shit the situation made me feel. I didn't have any huge dramatic falling out with anyone, or cutting people out of my life or anything, I just had to teach myself "This person has not got time for me right now" and not take it personally. And I really had to try hard to only do things that were in my best interests. I am naturally eager to please, in my desperation for friends (and relationships) and this was putting me on the back foot in a big way. I was sick of people taking advantage of me, not because they were evil necessarily, but just because they knew they could.
I also really made an effort to allow myself to do something I love. I had always wanted to learn to dance but never had the chance/guts. When I was at my lowest ebb I started classes and it changed me completely, it really gives me something to look forward to and has improved so many other aspects of my life, and given me confidence. I have met some cool people through doing it as well - not necessarily bosom buddies, but it's some sort of social contact, whereas before I could spend a whole weekend not speaking to a soul. It's easy to glibly suggest that lonely people take up a hobby, I used to get really annoyed at that as I felt so socially inept, but finding something you love is a good distraction. It's great that you have the charity work to keep you occupied :)
So while I am not entirely happy and satisfied, I am more at peace now. I still have wobbles, sometimes major ones, but I am learning to cope with my feelings.
I don't have any advice, just wanted to tell you you are not the only person in the world who feels like this. I am certain you are not lacking anything! And you definitely matter, even if people don't show you do.