I finally got to watch loving Vincent [1] (in the plane safely, but really glad they had it !) what a great movie !! I highly recommand it, stunning work ! Rarely have I had goose bumps this much when watching a movie ^^ and the end credits are really cool.
It discusses quite a bit the relation between Van Gogh and gachet. Very interesting. This article goes in a lot more detail tough.
The recent movie "Loving Vincent" goes into the last days of Van Gogh's life and his friendship with Dr. Gachet. It's a little less detailed/academic than this article, but does a good job at conveying the complexity of the situation and Van Gogh's struggles with mental illness. It's also visually incredible: every frame in the movie is a hand-painted oil painting. I would definitely recommend for anyone even a little bit interested in this sort of thing.