(1)Verse 1:

E
Sam
E
You've been waiting much too long now
   D
It looks like she's not coming home
E
Sam
E
You've been loyal
E
True and faithful
D                         E
All this time with being alone.
   A                         E
If I could get that same dedication
     A                        E
I'd give you everything in creation
B7
If she doesn't come back...

(2)Chorus:
              E      A   B   A
I'll be your substitute
              E      A   B   A
Whenever you want me (oo-hoo)
                             E      A    B    A
Don't you know I'll be your substitute
               E      A    B    (don't play second A chord here)
http://en.wikipedia.org/wiki/Substitute_(Clout_song)

Whenever you need me

(3) Verse 2: same chord progression as Verse 1

(4) Repeat chorus

(5) Middle Eight:
D                 A
Each day by your window you sit and sigh
E                  A
Hoping to see her face
         E               B
Oh, you might as well forget about her
     F#m     Abm     A        B7
And find someone to take her place

(If she doesn't come back...)

(6) Repeat chorus to fade