I am not the developer, and this is not reality, so I don't know what logic actually lies behind it. IMO, Alexis found the MC gesture (flower) attractive enough to feel moved to give him a kiss. Whether it was platonic, to cheer him up (because of the event and birthday), or other reasons, I don't know. In any case, I think it was important and right. That she later fell in love, she can not prevent it and it can happen. But Erynn:
mc "Did you go to Prom with ... Ethan?"
er "*Sigh* Yeah. Don't remind me."
mc "Why go with him?"
him "{i}(...){/i}"
he "You didn't ask me."
What is this???