Non of us are qualified to determine whether Captain Zaharie was suicidal or not, but from what we know about his devotion to aviation, I find it very difficult to believe that he would harm either his beloved plane or passengers if he wanted to end it all.
If he wanted to die doing what he loved, he would have hired a 172 on a day off and flown himself into the sea. In fact you know what? I don't even think he would have done that. He was so proud of his job and presumably his impeccable record that he probably would have found it difficult to 'blot' that record, even at the end.
And the co-pilot was on the point of proposing to his girlfriend, another Malaysian pilot.
I really do think pilot suicide comes way down the list of explanations of this mystery.