I don't quite get the vitriol towards Doumyou, she's obviously gonna fuck Tazune, but whether she's so opportunistic that she'll out Midori to him, I dunno.
I think the anger against Doumyou is because taking that picture was such a dick move. You see two people doing something intimate, and you whip out the phone and take a pic? Baaad.
Also, about whether Doumyou will snitch on Midori or not? Think of that picture as "Chekhov's pic" and you'll have your answer. ( ͡~ ͜ʖ ͡°)
Also @zensunni, I don't think they're married yet, just engaged. Nothing quite points out that they've been legally married yet for sure and the way they talk about their marriage coming up makes me think its more than the ceremony.
I'm a bit confused about that, too. Midori once gave "Tonoike" as her surname, but maybe that was a little joke. They don't act like a married couple at all.
My best guess is that they haven't tied the knot yet, and are planning to do both ceremonies on the same day: got to the City Hall, register their marriage, then go to some church or religious place and have a fancy wedding just pour le tralala.