Yes, it's a long one 
A work colleague (A) invited me and a fellow colleague (B) along to her wedding in France. Although I was a bit concerned about the cost/taking time off work, I said yes. We all met when we started working for the same company at the same time. I considered them both friends - though A and B were closer to each other, while I considered B a closer friend than A.
The wedding venue was in the middle of nowhere, and B and I found some nearby accommodation - two cottages set in half an acre of land, about a twenty minute drive from the wedding venue. Each cottage had two rooms, but as the second rooms had bunk beds, we decided to book a cottage each so we could each have a double room/bed. Neither of us particularly wanted to share a cottage (or sleep in a bunk bed) and were happy to shell out extra and make it a bit of a weekend away for us both so as to justify it. We would arrive on Friday and leave on Sunday, with the traditional wedding taking place on Friday evening and the white wedding on Saturday. There were no local taxi companies, but the landlady of the cottages arranged for a local homeowner to ferry us around between the airport, cottages, church and chateau (as neither B nor I had valid driving licences to hire a car).
Beforehand, A was expecting a special delivery from the States and asked me to bring it along with me (as it wouldn't arrive before she flew out), which I agreed to. She didn't want to ask B as she apparently didn't trust her to say yes or bring it. I thought of this as slightly odd, but didn't say anything. When the package arrived at our office, it was bigger than expected but I assumed this was down to overzealous packaging. When I got home and opened it, it turned out that the contents (wedding decorations) had not been packed properly and exploded in the box. I spent the entire night before my flight repackaging the entire thing (wrapping up each individual item with bubble wrap and tinfoil to keep them from exploding all over again). It also took up a whole suitcase, so it meant that I had to pay for extra luggage. No matter - the time and effort spent repackaging was a bit annoying, but I was happy to pay for it/take it with me - I certainly didn't ask A for money to cover it and even told her not to think about it as I was more than happy to help her out.
After a horrid journey (issues at the London airport with B not having checked in properly, me having to deal with a work emergency so was on calls all morning right up until takeoff, and a loooong ride to the cottages from the local airport), B and I arrived at the cottages. The landlady (lovely woman!) showed us around. As we were settling in, she then informed us that A had called her (not us!) before we arrived to book her wedding photographer (who was arriving later that evening) into one of the cottages for the weekend. By the way, A already knew that we had booked the place, but (having overlooked/forgotten to make any arrangements for her photographer) told the landlady to tell us to share one cottage, and offer the photographer the other, or for one of us to share with the photographer. No messages to either of us, or even a text, to ask if this was ok (let alone an offer to pay/reimburse us). A had a whole chateau for the wedding party, but clearly didn't want the photographer sharing with her/groom/family/bridesmaids. She also had other friends staying in separate accommodation on the chateau grounds, but didn't ask them either (or perhaps had tried to and was turned down).
B and I thought the landlady must have misunderstood and B asked me to call A, as neither of us were particularly keen to share with the other or with a stranger, especially having paid extra to have the place to ourselves. When I got through to A and tried to ask what was going on, she said that she was at her wedding ceremony rehearsal and didn't have time to deal with this - there was apparently nowhere else in the village that could accommodate the photographer and she accused me of being selfish for not wanting to share, and hung up the phone on me. Even though both B and I were annoyed/upset, B and I discussed and eventually agreed to share a cottage together, and let the photographer have the other.
As I tried to call A back to say it was fine and I would share with B, she and B were also texting each other without my knowledge (apparently, B made no mention to A that she also didn't want to share), and A then asked B to come stay with her in the chateau and let the photographer have her cottage, to which B (keen to stay in a lovely chateau, it would appear, rather than share a cottage with me or the photographer) agreed - her excuse to me being that, although we had planned the weekend together and she had agreed to share with me, she couldn't possibly say no to A's invitation as A "desperately needed her" 
B and I later got a ride to the chateau that evening for the traditional wedding (the white wedding was the following day) and as we stepped out, were "greeted" outside by the mother of the groom, who (without even saying hello) informed me that I was not to upset the bride further and curtly asked me to carry over and leave the suitcase with wedding decorations at the bottom of the stairs, while throwing her arms around B, inviting her into the chateau, thanking her profusely for "being such a good friend" and offering to show her to her room upstairs, with B lapping it up saying how of course she had come when A so clearly needed her ...
I felt very much persona non grata that night. When I tried to politely ask the MOH for a number for a taxi to head back to the cottage after the traditional wedding (B, who was now nowhere to be found, had sorted out the drive to the chateau and apparently not told the driver to come back to pick me up, even though I had asked her to), the MOH told me I should have thought about that before and would have to figure it out by myself, before turning her back on me. There were no local taxi numbers online and it would have taken over an hour on foot walking over unlit and unmarked private farmland (or longer walking the unlit roads) to get back. In desperation, I rang the landlady of the cottages who kindly came to pick me up herself (as our driver was in all likelihood already asleep).
Despite being upset at what felt like a bit of a ruined weekend, I still went along to the white wedding the next day and smiled and was sociable throughout the whole thing. Although I had this time arranged a ride back to the cottages, the photographer kindly gave me a lift back that night (and, on the plus side, he turned out to be a great guy and an even better drinking partner 
)
When I stopped off at the chateau the next day to pick up B en route to the airport, A came downstairs to say goodbye and handed me an envelope of cash to cover the cost of bringing her wedding decorations over. I hadn't asked to be paid for it, and it just felt like a pointed gesture after everything that had happened, and left a bit of a sour taste.
This happened some time ago, but I've just been invited to another wedding in France (a childhood friend's), which has brought it all flooding back. So, MN jury, who was being unreasonable? I've genuinely wavered between thinking:
(a) IWBU - I should have been a bigger person/better friend by just letting it go and agreeing to share in the first place, versus
(b) AWBU - I can't believe someone (bride notwithstanding) would book a stranger into a friend's paid-for accommodation without even asking/telling them, versus
(c) BWBU - I can't believe B managed to come out of it all smelling like roses!