Bolongi, 17, sings a romantic ballad he originally wrote to win back his ex-girlfriend.
"I was a relationship with a girl and it didn't go well. Apparently I was playing her, [but] I was innocent", he revealed.
"Me and my girl at the moment don't talk - there's tension there. I just hope she sees the song."
After the performance, Cowell tells the student: "So you played that song to her? That was out of tune and badly written."
However, the London-born hopeful blamed the on-stage support, claiming the microphone was "too loud" and gave him an electric shock.
Fellow lyricist Ryan O'Shaughnessy performed his own song 'No Name' on the ITV talent show last Saturday (March 31) to universal praise from the judging panel, and received the most online searches out of any contestant so far.
Britain's Got Talent airs at 8pm on ITV1, with Britain's Got More Talent following at 9.15pm on ITV2.
> Britain's Got Talent: Ryan O'Shaughnessy's 'No Name' girl revealed
> BGT Ryan O'Shaughnessy on 'No Name' girl: 'We'll stay friends'
Watch Ryan O'Shaughnessy sing 'No Name' on Britain's Got Talent below: