Her life had never been an easy one. Growing as she had, always ahead of her peers by leaps and bounds, one would think she would be proud. Possibly even arrogant. Not Cordelia.
No, she was a modest soul. She always tried to encourage the others to do better. Tried to help when she could. That made the other girls resent her, and the boys were infuriated by the fact that a girl could "show them up" so consistently. They were almost universally spiteful. Except for Sumia gods bless her. She just did her absolute best to make sure Cordelia's efforts to help weren't completely wasted.
They joined the Pegasus Knights together. Sumia was encouraged in just about all endeavors. Cordelia was dealt with hurtful taunts. Sumia was consistently given advice to improve her skills. Cordelia was relentlessly criticized over every little thing. Despite the favoritism, Cordelia never resented her only friend.
Not until she realized that Sumia held the heart of the man she loved. Even then, Cordelia did her absolute damndest to push her emotions down. She would never hurt Sumia. Not in this lifetime or the next.
Still, Cordelia couldn't stop herself from growing distant in the following years. When she heard of the amnesiac stranger whom was assigned as tactician of the Shepherds, a month had passed since they left for Ferox, Sumia in tow. The following weeks were a whirlwind of action, realization, and heartbreak.
When Cordelia finally had a moment to be alone, to grieve, she completely broke down. Sumia did what she could to help. It wasn't much, but Cordelia was thankful regardless.
She would later begin her interactions with the tactician. He was an observant fellow. Always asking the right questions, always knowing to stop before he pushed too far. The pain of her comrades' passing would never go away, but he made it so she could look back and remember why fighting for them, and everyone else the Mad King had taken from them, was so very important.
Cordelia didn't know when she fell for him. She had no clue what led to him to fall for her. Just that when Robin took a knee and presented a ring, she broke down once more. Only this time the tears were of joy.