I dont get it, why did they break up 8 years ago???

Because Peter thought Linus didn’t love him. He thought Linus slept with others and had a fiancé. He always felt bad that he had to keep their relationship a secret, but he tolerated with it. But when Linus said he was just a classmate to Linus’s father, Peter couldn’t take it anymore and they broke up. However, Linus has always loved Peter. But Linus is developing weapon so many people target him. Linus tried to hide Peter as to protect him but the lack of communication ruined it all.