With the nature of chapter releases, we've had literal years to stew on what could've possibly happened, what could be going through her head, what the actual reason behind their breakup that sets up this whole story could be.
But like, at the time and in the moment, wasn't the situation already being called absurdly silly and stupid? I recall this manga sitting at a rating at or maybe below 7, with dozens of comments on each of its earliest chapters expressing these feelings.
Here's the reality of it: Teenagers are absurdly silly, stupid, and impulsive. It's easy to see now how analytical Lemon has always been. It's easy to see how every time she insists she'll get a handle on things, it slips out of her grasp. It's easy to see she's never known how to be honest with anyone, including herself, and very nearly got there with Sunao.
But she didn't. I'm so glad (or should I say I hope I'm happy?) for all of those people who've never repressed their feelings, bottling everything up until the least deserving people who you know would still support you become your only available targets when you finally blow up. It's stupid in the moment. It's stupid looking back. It's stupid being on the receiving end. It's stupid being the one doing it.
Yet it happens. You cut people off. You distance yourself from them. You go radio silent. Instead of drifting apart, which might never have happened, you burn bridges instead. You're alone.
Some people never really recover from this social and mental self-sabotage. I know I barely did. But from the outset of this story we see how Lemon managed. She has a wonderful friend in Natsumi. She's that impressive Lemon again to the people around her, with enough careful distance to not hurt anyone, or herself, again. And when she finally comes in contact with Sunao, her desires and regrets resurface.
She knows she's in the wrong, and it's wrong for her to reconnect with this incredibly kind, understanding, if initially completely confused guy. But fortunately for her, she's stuck in a body swap rom-com, which means there's plenty of time to yearn and attempt to make up for lost time.
I...don't actually want Lemon to win. I do want her to be able to properly apologize to Sunao and be forgiven by him, and most importantly forgive herself. I want her to be able to wholeheartedly support Natsumi and Sunao once these idiots are freed from the rom-com curse and once her relationship with Sunao becomes a tiny bit less complicated.
I hope she's happy.