My (22f) boyfriend (22m) invited a platonic friend (female) on our trip together without asking me. How should I handle this?

My boyfriend and I (both 22) have been together for 8 months. We have our anniversary coming up next week and we planned to take a trip together. We planned to stay for 5 days in a different town and have a really nice time. We were talking about it for almost 2 months now and we were very excited.<br><br>I have exams in college this week and on Sunday, I was studying for my last exam yesterday and he asked me if I wanted to go to a bar with him and have some beers because I passed my most difficult exam. I agreed and we were having a great time.<br><br>He started drinking a lot and he told me that he invited a platonic friend of his (also 22, female) to go with us on the trip that we planned together. I got mad and he said that of course he will ask her not to go if I don't want.<br><br>I don't want her to go on the trip with us. During our relationship he never did smth like this and now I'm starting to question myself if she is really platonic or not. We have an argument and he told me that she is really platonic and if I don't believe him I can check his phone. He was angry and drunk and left the bar and went to his place. I don't know what to do. I want him to understand that I don't want her to go on the trip with us and I want to know if she is platonic or not.<br><br>&#x200B;