Why kill yourself before you can die in a war?
I feel he was more there to capture Kid alliance ( thanks to Apoo's info) than kill himself. To me he got obsess with way the people he respected died in great ways and wanted to create a memorable for himself.
Mostly saying this based on his obession with oden and his quote about death complete a person and also how he says Whitebeard did it right. To me the link between all those and his comments is how they had epic deaths the one piece world remember and keep them alive in people mind and he is chasing that.
To me the search for epicness is obvious. It cant just be I drank poison.
But you could say I'm just coping.