This is such a beautiful song!

The basic chords are:

|Cm*     (Ab)|Eb*        |Cm*       Gm|Ab (-maj7)  |

*with e-flat on top 

You should be able to figure the rest out for yourself - it's quite simple.

The riff goes something like this:

Bb - G - F - G          Bb - G - F - G       Eb - F - F - F