Sadly this double standard is just the way the Japanese entertainment industry is.
Look at what happened to Becky (popular media personality) last year: she gets outed as having an affair with a married male celebrity and her career instantly nosedived (seriously, average Japanese people were refusing to buy products she endorsed until the companies dumped her). As for the guy, he divorced his wife, but as far as I know his career didn't take a serious hit. (To be fair, part of Becky's brand was her "good girl" image, which obviously isn't the case for Tomoe, but the double standard is still there.)
Most female idols also have "no boyfriends, no dating" clauses in their contracts, although in practise this is probably more of a "don't get caught" clause. Apparently they're expected to keep up the illusion that they're "available" in order to feed the fantasies of their (male) fans. And yeah, said fans often do lose their shit if it comes out otherwise.
Hopefully Tomoe can either recover eventually or find a new career path. I wish her the best of luck in doing either.
My favorite picture of her is probably this one.
