It is a lovely song indeed.

I'm working on a sam smith song with one grace note. I've been ignoring the initial key before the main key. While I rehearse it I'll consciously add it till int blends in subconsciously like the other notes.

Its all muscle memory and I'll keep on with it.

As for playing by ear the first step for me is to get the main scale of the song then the progression follows.

I've found that some chords sound alike but the 1st chord is very distinct. Like Cmaj on Key C. But I could mistake it with Amin sometimes🙈...and Amin sometimes sounds like Fmaj and Fmaj like Dmin