"she'll make it up to me."

No she fucking won't.

If you seriously think she can, please please PLEASE tell me how. Tell me what in the world she could actually do to make up for forcing her alleged 'best friend' to endure a cheating POS and sit through a wedding that'll only remind you of the future you lost.

Seriously, WTF is this shit? I cannot believe more people here aren't calling her or the groom out for sweeping this whole thing under the rug or not making any effort here.

"It's MY day so I do what I want," oh fuck off, there is NEVER an excuse to treat a close friend this way. They should be kicking him to the curb, not ignoring you.

NTA by a long shot. Don't you DARE go to this wedding. If she really is your best friend, well then she better fucking learn to understand your feelings and not even get mad that you make this choice. Otherwise, congrats you've now got another toxic person you need to get out of your life.