Yes to all of the above.
And I'm 41, and still clueless as you felt when you were in your mid 20's. I've been 'dating' for 20 years.
20 years down the drain. I have nothing to show for it. Nothing.
Therefore, there's something magnificently wrong with me, and i'm just unlovable. No one wants me.
I understand what you are saying, that you don't feel like you can get to a lasting point in a relationship. I didn't start dating men until I was in my mid-20s. I felt so behind everyone else. I didn't have all of the experiences of the whole dating rituals that most people have by that age. I felt very awkward and insecure and did not pick up on social queues like when I guy looked at me a certain way or showed body language to let me know he was interested. I felt clueless.
There were many times when I felt like I was looking at the world through glass that I couldn't break through. Like I could watch everyone else have these enriching experiences that I could never feel for myself. Part of was fear: I was so afraid to put myself out there because of the fear of being hurt. Part of it is also that the places I was going were not the best to find someone interested in a long-term relationship. I'm not saying that you can't find someone decent at a bar, but there's a lot of people just looking for a hook-up and not interested in anything past a one-nighter.
Have you tried any sort of groups, such as volunteer work to meet people? San Fran is such a busy city with a lot of activities, I'm sure there are groups where you can meet people that share your interest. Don't give up and don't be so down on yourself. Don't give up and don't let the fact that you haven't found the right person convince you that you are unloveable. You are anything but.
It's a heroes journey, and you are the hero.
Loving Kindness Meditation will dramatically improve your spirits; give it a try for just 3 days: http://www.youtube.com/watch?v=sz7cpV7ERsM