It is not even like the victim's exact position in the house was not known or that she went to some unexpected or less expected place like a basement or a different room. No, she moved from an exact spot that is the most adjacent to the spot of the defendant and went to the most commonly intended place, especially from the sleeping bed or when one was about to leave (The later is probably what was intended). The defendant (I still call him the defendant because he was not convicted with what involves intentionally targeting the victim with full recognition of her identity) supposedly missed both noticing her absence then her existence or take that into account. He supposedly failed to do both of those things despite how doing that was needed to see if there was a reason for the fear to begin with. He supposedly did not check to search for the answer if there was a valid reason for his fear by checking for the existence of the victim in her spot.Then instead of the failure to do so becoming a reason emphasising even more that he should think if there is a real reason for his fear when the fact of recognizing a person in the toilet area presented itself to him he supposedly also failed to take into account that it could be his girlfriend and ignored this second one. All this allegation of fear supposedly because of a window he heard being opened.
One should also not be confused with the use of the word "fear" here. The defendant stated, which seems to be intended to answer how could he missed noticing the absence of his girlfriend from the bed, that he was too afraid to turn on the lights. Even without the fact that, absent other alternatives like trying to physically reach her, turning on the lights to check for the existence of his girlfriend was needed to see if there is a reason for the fear, that does not sound like what fear would naturally makes someone do. It seems that one would be more inclined to turn on the lights to see what is around him because of that fear. Even horror movies sound much more terrifying in dark than in lighted environment. Instead, the defendant is actually informing us with that allegation of a level of control over his alleged fear that overcame the pull of the much more natural reaction. Yet, despite such control over his fear he supposedly failed to take into account when he recognized someone in the toilet area that it could be his girlfriend.