Got to love the trope of the asshole who's trying to fix himself and becoming the wingman
It was bound to happen with any adult orientated relationship manga, let's hope we don't get the "return of the old flame" part
Honestly, with all the series now that try to shove "redeemed" assholes into an awkward love triangle with the protagonists, I'd gladly take a wingman.
Also, this is just my opinion and a gut feeling at best, but I feel like her old "relationship" might've been one where she couldn't contribute due to her personality, which would make it reasonable for her to want to "practice" with our MC so she could figure out where she went wrong and right herself for the future. She's the type that comes off mature despite having very pure romantic aspirations and some slightly airheaded tendencies, so I wouldn't be surprised if she got caught up in her idealism and rushed into a relationship with someone she couldn't connect with, and wound up hurting them in the process when she realized it wasn't what she wanted or hoped for. In that way, she could probably relate a lot more with our protagonist who we've seen trying and failing due to issues with his own personality that he has been working out through his practice with her as well. My hope is that they get past this, realize their similarities, and gain the courage to try things out with each other.
An old flame type arc could be possible, but I feel like it could just be a way to verify the changes to both of them from an external POV, and maybe even as a way of reassuring her of her growth as a person, with her old partner having already moved on.