Thinking and wondering.... wouldn't a BDSM dynamic work for them? I know both come from similar position and that might not work but still just throwing the thought out there.
I can imagine Ueno thrilled face when Moka says "...I'm gonna show you the technique that makes my ex cum in 3 sec, and many other techniques that I developed from countless sex experience"
It's taken too long to get to this point. Obviously, the first time he couldn't have gotten it up, he should have asked Moka to slap him, spit in his face, and insult him. That would have fixed the problem.
With Sagawa there is absolutely no love involved just pure frustration from both parties. And in any of the middle school flashbacks Sagawa is shown actually bullying Ueno.
Tsubumi isnt even dominant. I mesn Ueno pretty much took the lead last time they had a sexual encounter.
If the problem was just that, Ueno would onlybe atracted to Chisaki
Wait, Chisaki doesnt know that Tsubumi and Ueno had a sexual relationship. And Tsubumi didnt know that Ueno and Sagawa were in a sexual relationship. So Moka is ousting everyone.