fix ‧ a ‧ tion /fɪkˈseɪʃ ə n/ BrE AmE noun [countable]
1 . a very strong interest in or love for someone or something, that is not natural or healthy
fixation on/with/about
Carlo has an absolute fixation with the royal family.
a mother fixation
2 . technical a kind of mental illness in which someone’s mind or emotions stop developing