I have a feeling that it will be that something happened that either made her feel guilty or feel like a burden to him, so she in her mind she was leaving him for his own sake.
If you go back to chapter 88 and read from there it will refresh your memory. He was married to Raoul's sister, was using his status as a victim of Raoul to mooch off of people, and helped the national mages by convincing people to be sacrifices for their black magic.
Ya, I'm dropping this for now. Maybe I'll check back in a few months to see if this arc has ended, but it's just gotten dumb at this point. You can have drama without all the rapey vibes.
So it seems that just like him, she doesn't remember what happened the night they were drunk and just assumes they did it. It will be interesting to see what he said to her in chapter 10 when when asked him about what he remembered, whenever they reveal that. We may never know if they actually...
Why are thay talking about how Sakuta is pretending to date Koga of that only happened in wat was essentially a look Into the future that neither of them retained memories of? Is this essentially an alternate timeline where that future route was real?