AITA for cancelling my entire vacation because my bf wouldn't pay for the full 50% of costs after I said no to sharing a room with his new girlfriend?

I'm 25 (F) and my boyfriend (26 M) used to be really considerate and thoughtful and kind to me. We've been together for almost a year and like, I thought we were doing great. I thought we were on the road to having a serious relationship.<br><br>In fact, I was so sure we were on the road to something serious that I started planning a vacation for us. I chose a piece of my dream vacation for the spring, when I would have a break from grad school (I'm a full-time postgrad student). I was finally going to get to see the piece of the world I'd always wanted to see. <br><br>We did all our planning and booking before Christmas. I paid for my share of the flights and hotel, purchased insurance, and went into Christmas break thinking that this was going to be the most special relationship I had ever shared.<br><br>I did my best not to notice that he was acting strange, but he would just stare at me when I talked or would seem disinterested in what I said. Then, at Christmas, we spent the holiday at my parents' and when I went to give him a kiss goodnight, he slowly got up and started to kiss me back, but then he just turned around and said he wasn't the guy for me, he wasn't interested, and that was it. We'd been dating for almost a year! I cried because I was so hurt by how he was acting. Then after a few days of being upset, I decided that was it. I dumped him and said we couldn't be together anymore.<br><br>Well... I wasn't messing around when I said that, since I just blocked him on everything and told my parents I never wanted to see him again. The next time I heard from him was my friend telling me that she had seen him with some new girl from work and was pretty sure he had moved on. I didn't care, I still didn't want to know anything about him and wasn't going to try to win him back.<br><br>But then I found out that our vacation plans were still happening. When I went to cancel my trip because I wasn't going to travel alone, I realized that my ex was still going on our trip and he had paid for his share in full. I emailed him and asked him what the fuck he thought he was doing and like, tell me so I can get my money back, etc. I then found out that he was bringing his new girlfriend from work with him.<br><br>Apparently he thought that since I was the one who said we weren't going to have a relationship anymore, I could only request like 20% of the money back if I cancelled the trip. He had paid for more than 50% of the trip and wanted to offset my costs so he wouldn't have to pay extra. I was so angry with him. I said no, I wanted a 50% refund and was going to cancel the trip. He said I couldn't get my money back because he only paid for his part of the trip, which was 50%. I argued with him and he finally agreed to give me a 50% refund if I didn't cancel the trip.<br><br>He thought he had won and I only agreed because I wanted to keep my options open. He told me that he and his girlfriend were going to have a great time and they were going to be sharing a room the entire time. He said my girls would really like his friends so I should make plans to stay with them instead. I laughed and he was so dumb that like, I told him that girls were my friends too, so I could just stay in the room they booked and hang out with them the whole time. <br><br>Apparently he didn't like the thought of me in the room, because he texted me later and said he didn't want to drive to the airport with his girlfriend and me. I then realized he was still planning to drive me to the airport and pick me up. I told him hell no, I was never going to make him feel uncomfortable, so I was canceling the trip. <br><br>He argued with me and said I should have just stuck with the original agreement. I argued with him and said that was never an agreement and it was dumb that he thought it was. Then, I cancelled the trip. Like, I went through my airline and cancelled the whole thing. I didn't care if it cost me $500, I was so angry with him and I did not want to spend the next two weeks with him. I told him that and he called me an asshole and a crazy woman. <br><br>Am I the asshole for cancelling the trip? Am I an asshole for being angry with him? I don't think I acted like a monster or did anything wrong...