Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:6/8
K:Bb
['D G3', '|1 cAF']  
X:1
L:1/8
M:6/8
K:Bb
 D |:"Gm" G3 d2 ^F | (G2 A) (B2 c) |"Bb" ded"F" cBA |"Bb" dcB"F" AG^F |"Gm" G3 d2 ^F | 
 (G2 A) (B2 d) |"F" cAc f=ed |1 cAF F=EF :|2"F" cAF"Gm" G2 d |:"Gm" gag gf=e |"Bb/F" fgf f=ed | 
"F" cd=e fed |"F" cA^F"Gm" G2 d |"Gm" gag gf=e |"Bb/F" fgf f=ed |"F" cd=e fed |1 cAF F2 :|2 
 cAF F=EF |]:"Gm" G2 z A2 z | B2 z c2 z |"Bb" ded"F" cBA |"Bb" dcB"F" AG^F |"Gm" G2 z A2 z | 
"Bb" B2 z d2 z |"F" cAc f=ed |1 cAF F=EF :|2"F" cA^F"Gm" G2 |]  