I'm sorry you feel so awful. But I have felt like this many times and still here to tell the tale. Have had my heart ripped out by friends, family and lovers, and a broken marriage. Also left out of stuff, feeling I don't belong, not included etc. few friends, live alone.
Firstly, I determined that no one is worth anyone losing their life or sanity over, nobody. There are many, many decent people out there. Walk away from the ones who hurt you and who are not nice people. And with your dignity.
I now look to no one else to make me happy, I do it myself. I find my own happiness and am content with my own interests, past times, treat myself, generally enjoy life and in my own company. No expectations, and then everything that comes along is a bonus and very appreciated.
Keep busy, distract yourself, plan days out/holidays, go walking, join clubs, volunteer, read lots, box sets, cinema etc. etc. Go for coffee with acquaintances, make small talk, invite people to your home for a drink, dvd, or meal and let people know you are free.
Please don't give up, there is a world out there full of interesting things to do, places to go, new friends to meet. Hold on and keep posting too.