EDIT： Alot of you are complaining about the HP grinding, so here's a cheat code to unlock all 3 weapons so that you can see all the dialogue options without dying : gottastabthemall
It seems quite a bit of you are stuck on how to get the endings....so here is a breif walktrough.
Duke: To get his Insomnia Ending, make sure to save up HP and buy the 270 hp blue hilted sword. then when the option comes up, choose stab.
White: To get his Insomnia Ending, make sure to save up HP and buy the 270 hp PURPLE HILTED sowrd. Then when the option comes up, choose stab and let him go.
Joker : To get his Insomnia ENding, make sure to buy the red square thingy that cost 270 hp, then when the option comes, choose don't stab, don't stay. that should give you the true ending. choosing stay gives you the insomnia ending
the cheats for each character are in White's Insomnia ending. Duke's Insomnia ending, and the one true ending.