How does my choice affect the ending?

Solution 1:

When you kill your friends:

A sex scene with Citra follows. When it's over, she believes that she is now pregnant with Jason's child. Then she kills Jason with the dagger to give him the honor of "a warriors death".

When you refuse:

Citra is disappointed. Dennis is upset with Jason defying Citra and tries to stab him, but he accidentally kills Citra instead. The game ends with Jason monologuing about how the events of the game changed him.

Solution 2:

The difference is who dies and who lives, along with ending cinematic that show it.

if you save your friends Citra dies. If you go with Citra, your friends die.

First part of the video shows what happen when you pick Citra, it then continues with what happen if you pick your friends

Video