But why assume that an honest answer to those questions will make you feel better, rather than worse?
I think it's not that an honest answer will make you feel better. It's that a detailed honest answer is more likely to help you find tools for improving your situation, while a generic honest answer will make you feel bad and very little else. It's really just general steps for solving any problem.
Unattractive people have a much harder time finding romantic partners.
Much harder doesn't mean impossible! How much harder is it? How many people that look [a certain way] have partners and how many don't? Where did the ones that do have partners find their partner? Maybe you could look there. What other personality traits did they develop that helped them succeed at dating while looking [that way]? Maybe you could work on those!
And the partners they do find tend themselves to be unattractive.
This statement really requires data. Unattractive to whom? Probably not to them.
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.