First, this guy was raped as a young boy when he was 7. I don't know how that feels like or how it may have psychologically impacted my growing up years, but I can imagine it sucks really badly.
Secondly, the deceased came at him with a knife with the intention to injure and perhaps kill. So self-defense was necessary. However, stabbing the deceased 13 times was excessive. But if I were his lawyer, I would have argued that excessive force could have been a consequence of hysteria and panic, as well as high emotional stress at that point in time. The deceased was his lover, surely some element of passion was involved in the stabbing. You know how women lose it during periods of high emotional stress. This guy was effeminate and his ability to handle mental and physical stress could resemble that of a woman's.
Lastly, the reasons judge Rajah gave for his life sentence were based on the assumption that Ah Liang was an inherently evil, violent and mentally unstable criminal. Did he commit any crime before this? Was his disposition one of a violent, psychotic and recalcitrant offender who will be unresponsive to corrective training?
The crime watch narrator already mentioned that the forensics and criminal investigator had already established an impulse killing based on the blood splatter patterns and furniture knocked around. After the fact, Ah Liang placed a rug on the deceased wounds because "he felt guilty". Does this sound like a hardcore criminal to you? A life sentence was too harsh.