Ron Weasley regrets the day he let go of Hermione Granger. He has loved her since forever. Didnt realized soon. But during Battle of Hogwarts when she kissed him that was the happiest moment of his life. Then he screwed up. Instead of talking about their relationship he drowned himself in sorrow. Thats when she came. Carina Valentine A witch from Spain. Ron fell hard and fast for her. He knew he was breaking Hermione's heart.But he didnt care.
Then came a point when Carina accused hermione that she tried to curse her. Everyone knew Hermione was jealous. So it was easy to believe her. Gradualy Hermione grew distant from them. Harry eventualy regretfully choose Weasleys. It was between one person and a whole family.
Years grow by. His family saw articles in prophet regarding Hermione. Her work achievment,eventualy her wedding to Draco Malfoy,the birth of their first child.
As for Ron well Carina and he didnt last long. A few years later they broke up and Carina admitted she lied about Hermione as she was jealous.
But it was too late. Hermione broke all ties with them. She was already married. pregnant with baby no 2.
Even now Ron and Harry regrets throwing their friendship away.