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
['B,3 B,>CD B<dc B>GF', 'B>df f>dB g>fd']  
X:1
L:1/8
M:6/8
K:Bb
|: B,3 B,>CD | B<dc B>GF | B<GG G2 g | g>fd d>cd | B,3 B,>CD | B<dc B>GF | G3 F<DF | G<BD C3 :: 
 B>df f>dB | g>fd c>dc | B>df g>ab | B>cd c3 | B>df f>dB | g>fd d>cd | B>AG F<DF | G<BD C3 :|  