Somebody to Love
Right here, right now, that "somebody" to love has got to be yourself. It's been said a million times before, but I'm adding my voice to the chorus: You cannot love someone else, you cannot date the right person in the right kind of healthy relationship, until you accept and adore the person who you are independent of a partner. You can talk yourself into a circular logic situation of saying, "I would like myself a whole lot better if I were in a relationship," but I'm not buying it.
I typically try to avoid the, "here's what I think, but really you should go to therapy," strand of giving advice, but in this case, I think finding a productive relationship with a qualified counselor would be extremely beneficial. I say this not because I actually think that there's something "wrong" with you that needs to be fixed so that you can meet your beshert (soulmate). Rather, since, after presumably years of dating, that's the conclusion that you've drawn, I think it would be helpful to have a professional unpack that conclusion with you. You want to figure out what the "it" is, and exploring the whole range of who you are, how you present yourself and how you feel about yourself is going to be a step in the right direction whether or not there's an "it" that can be identified.
If you hate this suggestion and are cringing at the mere thought, or if you can't afford therapy right now, go to your local bookstore and peruse the self-help section. Lots of people have written lots and lots of pages about loving yourself and accepting yourself, and getting some of their perspectives could be almost as valuable as a real live therapist in terms of getting you out of your own head and focusing less on "the dating problem" in particular. After you've read some motivational literature, ask yourself what you really love to do, whether it's reading, cooking, biking, etc. Find an outlet to do one of those activities, alone or with a friend, but not in a way that's geared towards meeting a potential date. Make plans for the weekend that include activities or friends that make you feel good separate from any relationship potential they might create.
You might see where I'm going with this. Right now, you need to focus on yourself. You need positive social and creative experiences that fuel who you are and what you like about yourself. You need to stop beating yourself up about being single and you need to let go of the idea that being single is your fault. Give yourself a month or so and see how you feel. If you feel like you have a new perspective on yourself, go ahead and start considering dating again, but in a casual and low pressure way that honors your individuality. If you're still in the mindset of figuring out what's wrong with you that's keeping you from meeting "the one," then go back to the previous paragraphs and start over.
In the dating advice world, I've heard a lot of people say things like, "as soon as you stop looking, you'll meet him." While that may be true, and while that attitude has, in fact, worked for a number of people I know, don't think that you're going to stop looking in order to meet "the one," because guess what: that still counts as looking. Really honestly honor yourself and your time and your ambitions and interests. Take a break from overanalyzing every date you've ever been on. Try to enjoy life, and yourself, and then it won't matter what the "it" is, because there won't be one.