[spoiler]if you chose the revenge ending and kate died,it was still possible to date her o.O[/spoiler]
Here is a video-spoilers!
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I also found a comment on a video like this (not sure if it was this video) saying this glitch happens only if you dont save your game with the autosave after choosing the revenge ending
EDIT: here is the exact comment i was talking about. "It's a glitch that occurs if you don't decide to save your game after choosing the deal. I think." I think this guy means the revenge not deal,but anyways..