I agree with santiger she is not an idiot and the fact that you call her out on it because of this is idiotic of you.
Besides if you had read the article it states gillert grindelwald is the dark wizard who he fell in love with but maybe never got any reciprocation.
---She then explained that Dumbledore was smitten with rival Gellert Grindelwald, whom he defeated long ago in a battle between good and bad wizards. "Falling in love can blind us to an extent," Rowling said of Dumbledore's feelings, adding that Dumbledore was "horribly, terribly let down."----
I'm not surprised she didn't outwardly say it in the books as the backlash might be severe. Also i wouldn't think wizard society even with all its eccentricities would be very accepting so he kept it secret.