I was in your situation a year and a half ago. I was 24 and finally got the girl I've been wanting since 2nd grade. Like you, I had opportunitys and turned them all down. It was definitly worth the long wait. But to the point...
The first time we fooled around, just touching, she put her hands down my pants and I wasn't able to get an erection. Infact it did the the complete opposite. I shrivled as if it was freezing out. I was so embarrased. Since we had known eachother for years, we could easily talk and joke about it a few days afterwards. A few weeks later we had sex for the first time. Being my first time, I was so scared I couldn't get a full erection. Somewhat erect, enough to get in there. A minute later it completely went flacid, and that was that. I didn't come. Good thing to cause we didn't use a condom.
It happened the 2nd time we had sex, a week later. It bothered me to hell, but didn't her. She understood that I was new, and kept telling me it would get better. 3rd time came around, I lasted longer, but didn't come. 4th time...didn't come. 5 time...still hadn't come. Now it was starting to effect our relationship. I didn't want this to happen. One day, I put in my head that 'Tonight, I'm gonna come!' Not a single thought about what if I can't, or not a single thought about the other times. I just set in my mind and nothing else, that I'm gonna come the next time we have sex. We had foreplayed, and we were the most relaxed and comfortable we had ever been. Forgetting everything and just exploring eachothers mind and body. I came that night, and it was great!!! It was just all in my head. And its pretty much expected. Its something new. It took about 10 months for the both of us to finally feel 100% comfortable with eachother, and thats when the best sex of our lives started happening. Its like sport. The more you practice, the better you 2 get. OH! Don't chase the orgasm. It'll come. Hope this helps.