Ron nodded when Percy finished his sentence for him. She would do more than worry, she would show up at his flat and terrorize him for not coming to her the moment it was over. But, 'worry' was an acceptable enough word for the time being.
But then Percy kept talking and he kept talking and suddenly Ron realised that he wasn't talking about Ron at all, but himself and his relationship with Penny. Ron was about to ask Percy if he was alright but then his brother addressed him more directly. He felt his throat tighten up and he didn't really know what to say to him. It was a terrible thing to think of, losing Hermione, and if Percy still loved Penelope like Ron loved Hermione he couldn't even begin to think of how his brother was feeling right now. He had thought it was an ex-girlfriend, not a current love.
"Perce-" Ron croaked, his throat hoarse, "I'm so sorry. I-I didn't know. You never - I thought it was finished with the two of you."