I’ll tackle the sex issue, too.
“I’d never want to belong to a club that would have me as a member.”
Jim doesn’t think much of himself, and knows that the only women who could possibly consent to be with him must feel the same way about themselves.
Use your own experience here. When someone amazing is interested in you, you feel amazing. I remember in high school, if it turned out the person that had a crush on you was kind of a loser, you kind of wondered if that was the best you could do.....? And what did that say about you if that particular person thought that they had a chance with you? Yeesh. (ooops, been there, done that!)
Dagny and Francisco are internally calibrated to their own wonderfulness (to the point of obnoxiousness, really) so they would never consider being attracted to anyone that wasn’t perfectly wonderful, as well.
Boy, did you get that one right! Our first intimate time together, I saw stars.