Stories of obession?

Lust for Life (1956) - covers the life of Vincent van Gogh.

Fear (96)
Pretty standard obsession story but Whalberg, Petersen and Witherspoon were all very good as usual

Taxi Driver (76)
A Vietnam combat vet struggles with mental illness and his own anonymity in a big city he thinks should recognize him as 'the hero'

Here's one you might not think of: Mr. Holland's Opus. Glenn Holland had life-long obsession to compose a symphony.

Carrie - mum was obsessed with religion

Inside - killer was obsessed with the baby inside the woman

Oldboy - speaks for itself

Just thought of another. Manhunter or The Red Dragon

The Hand that Rocks the Cradle (1992)

Close Encounters of the Third Kind (1977)

Take Shelter (2011)

Nightcrawler (2014)

Conspiracy Theory (1997)

The Phantom of the Opera