All your life you've had a sense, however vague or pronounced it may be, that everyone else is living on Easy Street while you have to struggle and toil for every small gain. It may be true that parts of your life are a struggle, but you may be making them more so than they need to be. Believing that we are missing out on something is almost the same as actually missing out; the feeling that results is the same, anyway.
But regarding your love life, this can be a cyclical problem -- a self-fulfilling prophesy. You feel pessimistic about finding a love that will satisfy you, and so you don't try to reach out in a warm and loving way. Instead, you hold back, even when you're on a date with someone new and the possibilities still lie endlessly before you. Your reserved manner doesn't go over very well, and your potential sweetie goes home at the end of the evening with the feeling that things aren't going to go far...or, maybe they don't, but you convince yourself that they do! And that's that. You'll find much greater success in love if you can convince yourself to trust in the universe just a bit more, to bring you the love, nurturing and support that you need.