I've transposed it to C Major for some my friends to sing along. It's also much easier to play on C.
Anyway, here is the original key :
Intro:
D Dsus2 D Dsus2 D
Verse 1:
D A G D
She knows when I'm lonesome, she cries when I'm sad.
G D E A
She's up in the good times, she's down in the bad.
G D G D
And whenever I'm discouraged, she knows just what to do.
D G A D Dsus2 D Dsus2 D
But girl, she doesn't know about you.
Verse 2:
D A G D
I can tell her my troubles, she makes them all seem right.
G D E A
I can make up excuses, not to hold her at night.
G D G D
We can talk of tomorrow, I'll tell her things I want to do.
D G A D A
But girl, how can I tell her about you?
[ Tab from: http://www.guitaretab.com/l/lobo/53960.html ]
Chorus:
G A D
How can I tell her about you?
G A D
Girl, please tell me what to do.
G A D Bm A
Everything seems right, whenever I'm with you.
A G A G A D A G A
So girl, won't you tell me, how to tell her about you.
Verse 3:
D A G D
How can I tell her I don't miss her, whenever I'm away?
G D E A
How can I say it's you I think of, every single night and day?
G D G D
But when is it easy, telling someone we're through?
D G A D A
Ah girl, help me tell her about you.
Chorus:
G A D
How can I tell her about you?
G A D
Girl, please tell me what to do.
G A D Bm A
Everything seems right, whenever I'm with you.
A G A G A D A G A
So girl, won't you tell me, how to tell her about you.
D A G A