Develop a musical composition using the outlined alphabetical depiction of the structure and the provided theme.
X:1
L:1/8
M:6/8
K:Bb
['B3 dcB fdB BAB cAF FGA', 'BDF BDF dDF BDF ACF', 'fed bag fed']  
X:1
L:1/8
M:6/8
K:Bb
|: B3 dcB | fdB BAB | cAF FGA | BDE FGA | B3 dcB | fdB BAB | cAF FGA | Bdf b3 :: BDF BDF | 
 dDF BDF | ACF ACF | cCF ACF | BDF BDF | dDF BDF | ACF cCF | BDF B3 :: fed fed | bag fed | 
 bag fed | c2 d edc | fed fed | bag fed | fgf fed | c2 d"^da Capo" edc |]  