Boyfriend (25M) bringing his cousin (20F) on our honeymoon - how to feel about it?

Throwaway cause I’m dying of shame and my boyfriend knows my main account.<br><br>I (24F) met my boyfriend (25M) at a wedding where he was paired with me as a groomsman/bridesmaid. We got to talking and really hit it off. He’s traveled a lot for work and told me a lot of stories about his time abroad and was just really charming. We had a very strong instant connection. <br><br>A few months later, once the whole wedding party had gotten to know him, it became very clear that he was very close to many of the bridesmaids, who were all much younger than him. This was mildly problematic since a couple of them were still in high school, but I tried to focus on my own relationship with him. He was very sweet to me and I was infatuated. <br><br>We got more serious over the next year and he proposed to me. I was over the moon and we began to plan our dream wedding. <br><br>About a month before our wedding, I discovered he was still talking to multiple women from the wedding party. One of whom was his cousin. I hadn’t known they were related, but that didn’t really change anything for me. I did some more digging and found he was actively talking to multiple women, even though he had a fiancée. <br><br>I was devastated, but decided I couldn’t leave him. I loved him and was already married to him at that point. The wedding had already happened and it was hard to swallow my pride. I decided to try to make it work. <br><br>Fast forward to now: we are planning a belated honeymoon. We decided to go to Bali because it was a nice middle point for us. I had always dreamed of going to Italy, but he said he’d already been and wanted to try somewhere new. <br><br>I asked him what dates worked best for him and he told me, but said he would also need to bring his cousin with because she had always wanted to go and he didn’t want to disappoint her. I said it was our honeymoon and I thought it would be inappropriate to bring family. He said she’d be in a different hotel and wouldn’t be sharing our room, but I still said no. <br><br>He really pushed for it and offered to pay extra for her, offered to get me the spa day I wanted, etc. Eventually I said yes, but he took that as me being generous and letting him bring her and didn’t get me the spa day I wanted (which I didn’t expect but it’s annoying). <br><br>I hate this situation. I don’t want his cousin around either of us. But he says she’s like a little sister to him and he can’t disappoint her. I’m so confused and don’t know what to do. I don’t want to start my marriage off by fighting but I don’t want to be trapped in a hotel with his cousin for 2 weeks.