I hate the man my bestie is marrying

I have a love-hate relationship with my best friend that changes depending upon who she is dating. If I get along with her boyfriend, she and I are fine because we can do things together and our friendship stays intact. If I don’t get along with whoever she is dating, she tends to always pick her boyfriend’s side over mine and this leads to arguments, anger, and sometimes even long periods of non-communication. We have tried to address this in the past because we know it’s not good for us, but it always happens nonetheless. She recently got engaged to someone I don’t get along with, and I am already prepared for the possibility that we may not be friends anymore after her marriage. Is there anything I can do to avoid that from happening? I don’t want to lose a friend.
You’re right about this not being good for a friendship, because a strong bond like that has to be unconditional. If one of you isn’t willing to put in the required work to eliminate those issues, this isn’t going to be fixed because it is a partnership like any other relationship. You don’t have to lose a friend after marriage if you do whatever you can do keep things manageable, but there may come a time where you feel as if you’re the only one trying to keep this alive. I suggest you tell her one more time why this is important, and what your fears are, and ask her if this is as important to her as it is to you. Change after marriage is very likely but it doesn’t have to affect either of you if there is clarity about what you want to save and keep separate from anything else going on in each other’s lives.

My girlfriend always asks me to do things that she herself doesn’t ever do. How do I call out this hypocrisy?
You call it out by simply speaking your mind repeatedly until the message eventually gets through.