I'm not sure how far you are in the novel but Compeyson plays a direct role in the lives of Miss Havisham and Magwitch and these roles then affect the life of Pip. Compeyson was the man who left Miss Havisham at the altar. He was the reason she was so hateful towards men. She trained Estella to treat men poorly so Miss Havisham could get some kind of revenge on Compeyson. Compeyson was also the business partner of Magwitch. When he finds that Magwitch has returned to England, he contacts the authorities. He is the reason Magwitch is eventually captured and dies in prison. All of these action affect Pip. Pip's love for Estella is never returned because she is incapable of loving. This was because of the way Miss Havisham raised her in order to get revenge on Compeyson. Since Magwitch is Pip's benefactor, Pip loses all of his money and his "expectations" are dashed because of the capture and death of Magwitch. Thus Compeyson's actions have wide-ranging effects on everyone he is close to.