For my birthday a couple of months ago a good friend of mine kindly bought me a sailing lesson as I'd been saying I was keen to try it out. Our DPs are both into sailing and although they have met a few times and get on they haven't really had the chance to spend some decent time together yet, so the plan was that my friend and I would have the lesson together, and our DPs would come with us and go out on a separate boat too. We looked at all the dates we could do and settled on this coming weekend.
My DP told me he was going to watch his team's football match on the Saturday so to make sure it was on the Sunday instead. So we planned it for this Sunday and also decided to go for lunch afterwards at a nice pub. I've been really looking forward to it, especially as it's the first time we've done anything as a four, and said to DP last night that I was excited about this Sunday. His face fell and he said 'but I've got the football this Sunday - I thought sailing was on the Saturday?' I got out my diary (which I always keep up to date, unlike DP who 'uses his head' 
) and it clearly showed the football on Saturday and sailing on the Sunday. He then went red and said he remembered now that the game had originally been scheduled for the Saturday and then it got moved to the Sunday after we'd made our plans and he forgot to tell me.
So, I assumed that he would just not go to the game, given that we'd made plans with other people, it would be rude to cancel on them at such short notice, it was his mistake for not realising earlier, and he was going to the football on his own so wouldn't be letting anyone down by not going. Yes it was a shame for him to miss out but he could watch the highlights later and check the score during the game itself. He on the other hand wants me to just go without him - he says the football ticket cost him £50 and that I don't understand but he loves his team and has been really looking forward to seeing them. (He sees them about 5 times a year, I reckon). He says him not coming sailing doesn't stop me and my friend from going and her DP could either not come or could take a boat out on his own. But we have been looking forward to it as a double date and a chance for our DPs to get to know each other better.
So...which one of us IBU?? Thanks all!