I'm really sorry for your sadness. I can relate to much of it. I would ditto the suggestions for keeping a gratitute journal and volunteering. While I haven't kept a journal, per se, there was a distinct turning point in my own life when I started to focus on being grateful for things, rather than "happy" about them, mostly because it is actually possible to be grateful for bad things (to the extent that some of the best things in my life are actually derived from the bad). Beyond the obvious benefit to the community that volunteering provides, it's just a great way to feel good about yourself and to get outside your own mind once in a while.
For me, my long, long stretches of being single made me feel pretty unloveable. Couple my pathetic romantic history with a family (and, more speficially parents) that is, in a word, dysfunctional, and I felt very alone and lonely for much of my life. With the help of therapy, yoga (and a very spiritual yoga teacher), cycling, some great friends, and my own fierce determination to feel differently about my life and myself, I finally figured out a few things that worked for me.
Most significantly, I started to firmly believe that I was capable of loving myself enough to make up for my family and lack of a SO. That, in and of itself, was completely empowering. I also accepted that I was going to have to work at being happy. While it may come more naturally for some, I really had to make a conscious choice every day to do what I needed to do to be happy. Some days, that was as simple as going to a yoga class. Others, it meant really sitting with my thoughts and feelings. I had/have to be diligent about it.
Finally, I more freely allowed myself to have those sad and lonely moments without giving in to their full power. I used to try to stuff that sadness into a closet, for fear that it would simply overwhelm me. Again with the help of therapy, yoga, cycling and some good friends, I started to feel more confident in being able to go to those "dark places" without fear that they defined or controlled me. Interestingly, the more I allowed myself to feel lonely at times and to be "okay" with that, the less lonely I felt.
If my journey had stopped there indefinitely, I truly believe I would be a happy and content person. It certainly paused there there long enough that I can say that with a straight face. As it turned out, however, I ultimately did meet someone with whom I plan to share the rest of my life. He's truly been the icing on what was already turning out to be a darn good cake.
Anyway, that's my story. I share it with you to give you some hope that you may not always feel the way you do today.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher