So me and my friend have been really close since we started middle school. She's the closest person to me outside my family, and the closest friend I've ever had. She's in a serious relationship and has been for a while, so since a friend of ours got married over the weekend she's had weddings on the mind. I teased her about basically planning her whole wedding since then and she told me she'd planned nearly everything, except who her maid of honor would be. She basically told me that I would only be hers if I promised that she'd be mine. For some background, she's not close to any of her family and has no close siblings. I'm her closest friend, so when the time comes then I'd assumed she'd pick me, because there really isn't anyone else who would make sense. In contrast, I come from a very large family, and despite many brothers, I only have one sister, who I'm pretty close to. I told my friend many years ago, probably around 8th grade, that I'd like my sister to be my maid of honor when I get married because she's my only sister, and that made sense to me. She knows this, she was offended at the time, but she knows it's important to me. The last time we talked about it I basically just said that there's no way that I'd be able to plan anything about my wedding now, and that we can worry about it later on. After she made that condition today I just made a joke about how she'd be waiting a long time to tie the knot if she had to wait for me to do it first, and then after I didn't promise her that she stopped texting me back at all. She'll get over it (I'm not scared she won't talk to me or anything), but is it unreasonable for me to expect to be her maid of honor if I can't promise she'd be mine, or is it unreasonable that she's making a fight over something that probably won't be an issue for at least a decade? (We're only 20).