Why did I lose the game?

So I have a saved game on 1.1.1453. If I unpause the game, I lose a day later. As far as I can tell I didn't die. I have 3 sons, one of them is my heir. No losing wars that could suddenly claim all my land or anything.

Any ideas? Is the game simply over on 2.1.1453?

(It's in german, I can translate anything if you ask for it in the comments).

So I've found a little part in the wiki beginners guide stating

CKII is a sandbox game and has no strict winstate. As long as at least one landed member of your dynasty survives (of at least the rank of count), the game will continue until 1453 and at the end you will get the same dynasty score screen (comparing your dynasty to some historical dynasties) you would get if you had resigned earlier. There are achievements that can give goals to strive for, but other than that players must choose for themselves where the emergent gameplay will take them.

Which I didn't spot earlier because it doesn't say so on the game over wiki page.

(I hadn't seen that when asking, but it seems to be the solution.)

A game of CK2 ends when

• no person of your dynasty could inherit and your House goes into an end.
• you reach the year 1453 (which is your case here).