Hi Chibi,
I looked at the video, and you're saying since Gluttony was your last to date, you should get his true ending, correct?
Even if Gluttony is your last Sin to date, you can only get his true ending if you don't make bad choices on his route. But if you do, you'll get a regular ending, Greed will text you, and then the game will end.
I think that is what you're asking about ? Let me know ( ^^)/