Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:3/4
K:G
['BG GD{B,} CB, A,A AE F/G/A/F/ BG', 'Gg dc/B/']  
X:1
L:1/8
M:3/4
K:G
 BG GD{B,} CB, | A,A AE F/G/A/F/ | BG GD{D} CB, | A,G GD E/F/G/A/ :: Gg dc/B/ c/B/A/G/ | 
 F/G/A/B/ AE F/G/A/F/ | Gg dc/B/ c/d/e/f/ | gG GD E/F/G/A/ :|  