In common sense, if your friend tells you she broke up with her ex because he cheated, but is now dating someone new. Would you really need to encourage her by mentioning that ex?
You probably wouldn't need to talk much about the ex, right? Instead you'd eager to know and ask about the new guy, right? Also, you probably wouldn't worry about her who's been taken care by her new boyfriend already, right?
In opposite, you should be worried about her if she's single and still can't get over her ex even though he cheated, right?
And in the depth of your heart, you don't believe the ex cheated because you know he's a good guy and he's also your crush. So, you confessed to her you've ever fallen in love with the ex too and make it a joke to cheer your friend up, right? You still can't hate him, the ex, but you've to believe your friend that he cheated at this moment. (You'll try to find the truth later)
Anyway, It's also possible that Sakura has the fucboy as a new boyfriend but didn't tell Mio and Nagi and pretended to be a victim letting these two girls soothe her !!!
But do you really think Sakura is that kind of wicked person?
If Sakura hid the fact that she was dating the fucboy just to make herself look like a victim, then she deserves the hate and the backlash because that would make her truly evil. That’s the behavior of a villain, not a heroine. LOL