I'm going to leave my fiance after surgery
What makes you think you need to leave your fiancee after your surgery?
The surgery changed me, and she will never react like I want her to react.
It is hard to say how anyone will react after surgery. It might be hard for them to express their feelings, but you should talk to them about it.
I never expected this but I'm too much of a coward to stand up to her, we don't have the same level of loyalty anyway.
I'm sorry you are going through this. It's not okay to leave a relationship because you are scared. Everyone gets scared, but you need to communicate with one another.