Quick, accept her confession before the ex interferes.
Becoming happy with another girl is a good way to take revenge on Hanabi, but of course the main reason should be because he likes Fumi back. And I think he does, because what he just did was a risky move that went above and beyond to clear her name.
I'm just a little disappointed he couldn't tell her earlier about his plan, but now he did. On another note, it's more disappointing that the fallout of the incident stopped with Erika's parents who were even less involved than Hanabi, who got away scot-free.
It was satisfying to see him not trust that useless teacher, though. And I'm still suspicious of her, it's like she's got an absurd bias in favor of bullies and was only forced to apologize and reprimand the bully because she was cornered by the exposé.
Thanks for continuing this series, I think you've done a good job so far.