well Frankie,

It took for myself a couple of years to be able to " hear" the jazz harmonies.

This song is in fact really structured in terms of harmony:

the tune does employ successively different key tonalities centers :

1) bars 1 to 8 : /G RMM (melodic minor) : Gm-Bb, /C min nat: Eb-G7-Dmin7b5-Eb-Bb7-Cm

2) bars 9 to 16 : /AHM(harmonic minor ):E7b9b13 -Dm11+ - B min7b5 (Locrian 6)-Am ,/D RMM :Bb13-A7b6-Emin7b5-Dm

3) bridge (bars 18 to 24) : /Bb maj :Bb-EbmAb7-,/Bb RMM :Csusb913-Bbm-Db,/G min nat :Em-A7-D7

4) bars 25 to 32 : same as 1)

Then ,on this kind of harmonic construction,you have to construct a "climax":like a painter,you have then to choice colors..
Jazz at beginning of his mastering is NOT a purely improvised music ..until your brain begin to react like a computer ..and then,after some (many for me !) years,it becomes slowly a part of you

cheers !
milou