I think this is a pretty common problem. I even know men who have trouble coming during sex.

Personally, I can easily and reliably bring myself to orgasm in five minutes alone, and before becoming sexually active I always assumed it'd be that easy with a partner. Boy was I wrong.

I know what you mean about performance anxiety - when my boyfriend is going down on me and I know I'm gonna take a long time, I start to get nervous that he's going to get tired or sore, or just that he's not enjoying it anymore. Despite his constant reassurance, it took some work on my part to teach myself how to come with a partner.

Here are a few suggestions:
1. Masturbate during partner play. Do whatever you do alone - whether it's looking at porn or humping pillows or playing with your favorite vibe. I like having a vibrator around during sex in case I'm having 'one of those days' where I just can't seem to make it; it helps lift the pressure off of both of us, and I'm more able to relax knowing I have a backup in case he gets tired.
2. Speak up! Teach him exactly how to touch you, and be vocal when you want more/less/something different. Don't wait for it to start feeling good - if it feels bad or even neutral, do something different or stop.
3. Fantasize. There's nothing wrong with thinking about another situation during partner play. Laying there thinking, "I'm not close yet, oh God this is gonna take a long time..." etc. is counterproductive. Ban those thoughts from your head and focus on something else, whether it be your partner, your breathing, or some sexy situation you've thought up. (My technique for getting the distracting thoughts from my head is a mantra: "More, more, more,")
4. Don't make orgasm your goal. Similar to #3: don't time yourself, don't think about time, don't think about orgasm. Approach your play for what it is, not as the means to an end.
5. Talk to your partner. Make sure he knows how you feel about this. Brainstorm some ideas to help you relax together - maybe more foreplay, a nice massage, mood lighting, or music?

Anxiety is a huge orgasm killer. Do what it takes to help yourself let loose - even if that means accepting that you won't always have orgasms at first.

Good advice prax... as a younger man I used to get a llittle upset if my partner masterbated herself during foreplay. I am now a bit older and have more experience and understanding. I now encourage my wife to please herself during foreplay or anytime during our love sessions. Please ladies you also have to tell us what feels good and what does not. All of my lovers have had different things that have gotten them off or got them extremely excited.

Thanks for the tips Prax, I'll definitely have to try out that mantra (since I get stuck with the "oh gods this is gonna take forever" thoughts and frustrations) and see if it works.

Thanks, Prax. The advice came a bit late (he'd already dumped me for a couple a months by that time), but I will definitely follow your suggestions whenever I get involved again.