Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/16
M:3/4
K:Bb
['G4 G4']  
X:1
L:1/16
M:3/4
K:Bb
 G3 G | c4 c4 (e2d2) | e4 G4 G4 | c4 c4 e4 | d8 e4 | G6 F2(E2D2) | C4 D4 C3 E | 
 G4 G4 (3A12 .A12 .B12 .A12 .B12 .c12 | .c8 c4 | G6 E2 D4 | C4 D4 C3 E | G4 G4 (A B3) | c8 G2G2 | 
 c4 c4 (e d3) | e4 G4 (G3 A) | c4 c4 e4 | d6 z d e3 e | G6 F2 (E3 D) | C4 D4 C3 E | G4 G4 (A c3) | 
 c6 c2 A c3 | G6 E2 (D3 C) | C4 D4 C3 E | G4 G4 (A c3) | c8 ||  