I used to obsess over this too, and it ruined one of my relationships (as I started acting out from the fear). Unfortunately, there's no quick or direct fix that I know of, like a "pill" to solve the problem.

Over time, though, I've learned how to deal with it better. It hasn't disappeared - I still feel strongly insecure at times - but not so much that I can't just sit through it til it goes away.

But aside from time and experience, one thing that has really helped for me is dating people I'm already friends with. That level of security and trust, and having already established strong communication, remove a lot of the pressure to perform I would otherwise feel. Which, ironically, probably makes the sex a lot better for both of us.

So, my advice would be this: when you feel kind of attracted to someone, focus on building a friendship with them (only if you genuinely like them as a person, though). To take the pressure off, just make a rule with yourself that you're not going to try anything with them for a while, if ever. Thus, if nothing ever happens it isn't a "failure", it's by design.

If you do this, I believe that over time you'll feel more confident and self-assured, and moreover there will increasingly be a chance that a friend develops feelings for you - someone who you won't worry you have to impress, since they got to know you and liked what they saw. If you're lucky enough to have this happen, I'd expect that that type of relationship - friend turned lover - would be healthy for you, and you'd find yourself worrying a lot less about these things than you normally do. Just a guess, though, and one that's heavily informed by my own personal experience.

What do you think? Does what I've said apply to you? Does this seem helpful, or not really?