Namely that the person you are betraying considers you trustworthy.

If they already expected you to mistreat them, then it's not betrayal, though it's still ####ty behavior.

By playing their game and accepting their authority, we place in them a measure of trust. Among other things, it's reasonable to expect that immortals will not mess with my life outside CF.

Even if I am a bad player, which I always tried not to be, it's still a reasonable thing to expect.