Yeah, I was gonna say pretty much exactly this. It may be the advice the most likely to lead to general dating success over the long term, but it really doesn't help me deal with my situation right now. (Though I certainly didn't downvote it.)
If It seemed like I meant he should ditch her and move on, I apologize.
My main point was basically "what would future me say to past me when I felt that way?" And that most definitely is "Don't worry, it'll work out." Because that's the best advice of all.
It'll either work out positively in which case you'll have a good relationship, or it'll work out negatively in which case you'll have some good memories and some hard lessons learned for next time. And if you can think of those let downs as one more layer of thicker skin to help you not worry about them, you'll be better off.
I know it doesn't seem that way now, but there really is nothing to worry about.
I started going out with a fantastic girl a couple of weeks ago. Everything is great, except that whenever I've sent her a text message or email requesting something and haven't received a response yet, I experience significant dysphoric anxiety, fearing that her response will be not just "no" but "no and I don't want to date you any more". This is due to brain chemistry or personal history, take your pick—either seems like a possible explanation to me. But there's certainly no evidence supporting the idea that this is likely to happen, nor is the anxiety helping me prevent it or helping me in any other way.
Does anyone have evidence-based advice, or pointers to same, on dealing with this kind of issue? It is the only splotch on what have otherwise been the best two weeks of my life.