Develop a musical composition using the outlined alphabetical depiction of the structure and the provided theme.
X:1
L:1/4
Q:3/4=100
M:6/4
K:Bb
['B2 B B3/2 c/ d c A', '=e f2 f f3/2 e/ d c']  
X:1
L:1/4
Q:3/4=100
M:6/4
K:Bb
 G | B2 B B3/2 c/ d | c A F F3/2 G/ A | B2 G G3/2 A/ B | A3/2 G/^F/=E/ D2 A | B2 B B3/2 c/ d | 
 c A F F3/2 G/ A | B3/2 A/ G A ^F2 | G3- G2 :: =e | f2 f f3/2 e/ d | c A F F2 f | g2 a b3/2 a/ g | 
 f d d d2 =e | f2 f f3/2 e/ d | c A F F2 A | B3/2 A/ G A ^F2 | G3- G2 :|  