reality vs fiction
Soooo.... apparently there are 2 very different accounts of the story.
Here is one by Shirley's relatives - https://shadowandact.com/the-real-donald-shirley-green-book-hollywood-swallowed-whole
And here is one which has more of the narrative by Tony Lip's relatives - http://www.historyvshollywood.com/reelfaces/green-book/
And here is a video of Donald Shirley - https://youtu.be/DY69eoacdLg
He sounds....err... a bit different from the dude playing him in the film.
There is apparently a documentary being made about Shirley - with him telling his story in his own words - it's called 'Let it shine'.
Anyways.... like I said, the video of real-life Donald Shirley shows a very different character - VERY different. In fact, I'd argue that the character we see in the film is by far more charismatic and sympathetic than the real-life Donald Shirley, but that's just my opinion.
In the end though - it seems like there was no friendship, and Donald Shirley had a very different personality than the one presented in the film.