Exactly what I was thinking. I feel sorry for Matsuri not being with the guy she loved, but I'm happy she left to find happiness somewhere else. I think this is the first time I've ever thought that it was good for someone to give up on their love.I respect Matsuri for going NOPE! She should have done it sooner, but it's way better than the alternative of trying to double down. It could have gone far worse for her. With any luck, she'll never appear in this manga again and it'll all just be a terrible memory for her.
As for the poor onii-chan though, he's stuck on Shizuku's wild ride. Poor guy is just trying to be a half-decent brother despite his depravity, but Shizuku's going to grind down his soul until he's completely and absolutely hers.
You're forgetting that the first thing the brother did when he realized that he was about to cross the line was to get away. He was perfectly willing to live alone and depressed as long as he couldn't lose to his temptations and defile his own sister. Maybe he should have been more forceful in making sure his sister wouldn't live with him and be in a position to psychologically manipulate him, but he wasn't expecting Shizuku to be a degenerate.Damn... at this point, I don't even think the sister is at fault for how he is. She obviously played a part to make him like this, but let's not forget that he was like this BEFORE she met him. That being said, they are BOTH really fucked in head to do this stuff with each other, so I think they both deserve each other and I'm glad Matsuri got out when she did, she really had no shot from the start. Now that he realizes he's beyond help, I wonder how this will play out, considering how he got a hint that his sister might like him too. I'm really interested to see how this turns out.