So I've been seeing this girl on and off now for a year now, we started having sex about 5-6 months ago and it was always fun... for me, a few weeks ago when we were having sex, we changed to 1 of her preferred positions (her on top with me thrusting from underneath) after doing this for a bit I went faster and it seemed like she was about to orgasm, but right as it seemed like she was about to she literally jumped off, initially I figured she just wanted the pleasure to last longer and didn't think anything of it, but it happened 4 more times, I asked why she wouldn't just let it happen and she responded with "because it hurts" and then got back on... I asked her what's the point then and she responded with "because it's fun" we finished and that was the end of it, we've had sex multiple times since then, but I never delved deeper into the issue, but considering I want to eventually be in a relationship with this girl I want to know what I can do to resolve this issue if that's even possible.
Is it possible to have a painful orgasm, painful enough to not want it to happen?

She needs to see her doctor (especially if this is a 'new' problem) to make certain she is healthy and not experiencing any medical/physical problems.

These questions are for her to answer to help narrow down what the problem might be:
1. Does this happen when she masturbates?

2. Does it happen if she is using a vibrator/toy?

3. Does it happen in all positions or just when on top?

4. Did it occur with other partners?

This is something she is going to have to begin figuring out on her own. But yes, an orgasm can be painful at times. Usually because of physical issues such as bladder infections or bruised muscles. That's why she needs to get a check up.

Good luck.

Thanks for the help!