Complex sentence: Besides skipping school and getting into fights, he did badly in his GCE Ordinary Level and even failed to complete his Singapore-Cambridge GCE Advanced Level, he also went into depression from what he perceived to be a goal-less existence.
Split into simpler sentences: Besides skipping school and getting into fights, he did badly in his GCE Ordinary Level and even failed to complete his Singapore-Cambridge GCE Advanced Level. He also went into depression from what he perceived to be a goal-less existence.