verb

cause (someone) to develop an obsessive attachment to someone or something.

he became fixated on the idea of a Third World War

obsessed with,preoccupied with/by,obsessive about,single-minded about,possessed by,gripped by,in the grip of,engrossed in,immersed in,taken up with,wrapped up in,devoted to,dedicated to,enthusiastic about,fanatical about,infatuated with,besotted with,focused,keen,hell-bent,hung up on,hooked on,gone on,wild on,nuts about,crazy about,potty about,dotty about,wackadoo,wackadoodle