The quickest way out of this of course would be to look for folks who are in need, the sick, the aged, even the lonely and offer your time being a companion to or helping them. You sound very educated and have many interests so perhaps the people you are trying to be with are not the type of people who can appeciate who you are - but for some reason you are drawn to them, seeking acceptance. Since this is a pattern from childhood is it possible you are drawn towards the types of people who are bound to reject you? Usually, we feel unappreciated by others because we are expecting to get something back - once you go into a situation with the attitude of giving rather than receiving you will begin to develop an appreciation and confidence in yourself that is not based upon what others are giving YOU, but the truth of who you are and what YOU are doing to add to the good of the life of someone else. Almost every unhappy person I have spoken to has pulled back in rejection and become extremely focused upon self. This is natural as bitterness and loneliness creep in, but again, the quickest way out is to be of good use to another person. There are many people in much worse scenarios than you are who are poor, crippled, aged, lonely and rejected on levels that are no doubt much more severe than your own. These are people who pray daily for a word or smile and who you can probably relate to on a lot of levels. Maybe they are shut ins or folks with no family. Bringing by books, cookies, meals, visiting those in the hospital, old folks homes, so many places you could be where people would look forward to your coming, your visit, your kind word, helpful advice, etc.
I think you would find this both rewarding and revealing. It would help develop aspects of yourself perhaps you have forgotten about. There is nothing worse than giving of yourself in a place where no one really wants any part of it. Trust me, there are many people on this planet who are dying for a visit, a kind glance, the gift of a 20 minutes conversation. Start looking around for some of them and you might find by helping them a lot of your loneliness and feelings of rejection dissipate.