Masters sell their souls to demons.. for their petty revenge.. Once Claude tried you're blood he wanted you.. and only you.. so he tried to erase your memories but couldn't as you had sold your soul to another demon called "Sebastian"

he then manipulated you into thinking Sebastian SA you and killed you're little brother which is why you order Sebastian to stay out of your sight but to protect you he disowned that order..

CLAUDE : Tck Tck "such a bad butler to demon kind.."