Synonyms of one-track
fixatedIf you accuse someone of being fixated on a particular thing, you mean that they think about it to an extreme and excessive degree.
• As a child, he was fixated with video nasties.
obsessedfascinatedpreoccupiedcaptivatedattacheddevotedabsorbedcaught up insingle-mindedsmittentaken up withbesottedwrapped up inengrossedspellboundinfatuatedmesmerizedhypnotizedhung up on (slang)monomaniacalprepossessed
obsessedIf someone is obsessed with a person or thing, they keep thinking about them and find it difficult to think about anything else.
• He was obsessed by science fiction films.
Thesaurus for one-track from the Collins English Thesaurus