Utilizing the provided musical theme and letter-based structure, compose a piece of music.
X:1
L:1/8
M:6/8
K:Bb
['B FDE F2', 'B,2 f fdB fg_a |{_a} b3- b2']  
X:1
L:1/8
M:6/8
K:Bb
 B | FDF F2 B FDE F2 B | cec BdB | cAF TF2 B | FDE F2 B | FDE F2 f/e/ | dcB FBA | BFD B,2 :: f | 
 fdB fg_a |{_a} b3- b2 Tb | g=ec egb |{b} a3- a2 g | fbf dfd | ege cfc | dcB FBA | BFD B,2 :|  