Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:6/8
K:G
['B3 cBc ABc e2 d B2']  
X:1
L:1/8
M:6/8
K:G
 (B/c/) |"G" d2 d dBd | gfg B3 |"Am" cBc ABc |"D7" e2 d B2 c |"G" d2 d dBd |"G" gfg B2 g | 
"D" fed ecA |"G" G3 G2 :: (B/d/) |"G" g2 g gfe | dgd B3 |"Am" cBc ABc |"D7" e2 d B2 d | 
"G" g2 g gfe | dgd B2 g |"D7" fed ecA |"G" G3- G2 :|  