Harry should have been less forgiving to Seamus after he betrayed Harry when Voldemort returned.
Harry and Ron went to the hall together to play some chess. Just then, he heard a familiar sound. Harry turned around, to his shock he realised that it was Seamus, the boy who betrayed him for not believing him that Voldemort returned.
"Look, Harry, I am sorry for not believing you, I see now that Voldemort is actually back, and you are telling the truth..."
"YOU SEE IT ONLY NOW!" yelled Harry. "YOU ONLY UNDERSTAND IT NOW! YOU ARE A FOOL WHO BELIEVED THE DAILY PROPHET THAT I WAS A LIAR AND DUMBLEDORE TOO! YOU ALSO CALLED ME A MADMAN!"
"I am sorry..." said Seamus, stunned. "I mean... I.."
Before Seamus could say another word, Harry interrupted him, "Don't give me excuses. Don't try to say you unintentionally did not believe me. You should have known, I brought a fucking cup back to Hogwarts with Cedric's dead body, I went through so much trauma, and heck you said that no one was there when Cedric died."
"I am sorry, forgive me please." Seamus replied.
"No I will not. Anyway you aren't my best friend either, we were only just mere friends, and you on the other hand betrayed me when Voldemort returned just like nearly everyone else did. You believe in those morons and think of me as a madman. Now get out of my sight!" Harry said fiercely.
"Fine, I will, you idiot." Seamus snarled.
Ron shouted at Seamus, "Shut your mouth, you prick."
Seamus walked off sulkily. He had paid the price for his betrayal.