Well, I'm not sure of the exact details of Komi San's parents' love story as it might not be fully explored in all aspects in the original work. But generally, it could be a story of how they met, perhaps through mutual friends or in a common place like a local event or school. They might have started with simple conversations and gradually discovered their mutual interests and feelings for each other.
One possible key event could be their first meeting. It's often a crucial moment in any love story. Another might be when one of them first confessed their feelings. Maybe it was a simple but heartfelt moment like a handwritten note or a sincere conversation.