Boyfriend wants to bring his girl best friend

Me and my boyfriend have been planning a vacation around Christmas/new years to go visit his family in Thailand. I’ve already met his parents and siblings, but the rest of his relatives lives there. All of his family have expressed how they want us to come down for Christmas and visit them because they want to meet me. Yesterday he told me that he had been talking to his girl best friend about our trip and she asked to join us. He explained to me that her boyfriend was planning a boys trip and that she also wanted to go on a vacation. She doesn’t have any other friends (for a good reason). She had said that me and her could go around and do girls stuff while he could stay with his family and drink beer. He just agreed and laughed because “I do like to drink beer though”, like he actually thought it was a good idea. He didn’t tell her no and that this was a special trip between him and me. He seemed like he was actually considering it. I have talked to him before that i’m uncomfortable with how close they are and that he needs to step back a little for the sake of our relationship. He knows very well that I don’t really like her, we almost stopped dating during our first month together because of how they were too close. There’s no way in hell that his girl best friend is joining this trip and if he’s actually serious about inviting her I don’t know what to do.