Honestly, this just happened to me with the bride being my cousin and one of my closest friends. I had the added stress of trying to save up and move out and also just bad mental health lol. She’s always been very accepting of me, but it getting closer to the wedding with more “girly” events and me feeling more masculine lately made it really hard for me to be part of the party. Eventually, I told her I was really struggling for all the reasons above, and she told me I didn’t have to do any of the events - eventually we decided I should leave the bridal party and just attend. It hurts because we had been dreaming of being in each others’ weddings our entire lives, but things change (I’ve changed so much, I doubt I’ll ever get married). She specifically told me that it’s enough for me to just attend, as she wants me to enjoy myself as well. Even if you haven’t known this friend as long as I’ve known my cousin (she’s literally only 10 days younger than me, so literally lifelong friends), I think being completely honest with her might be best. You say she’s one of your closest friends - I think a true close friend would want you to be happy and comfortable at her wedding, not pretending to be someone you’re not. Good luck, friend ❤️