My best friend/boyfriend [21M] of several months is going away for the weekend with his ex-girlfriend [20F] so that they can "talk". I [20F] feel disrespected and incredibly upset.

We met about a year ago and become close friends quickly. He was dating the ex-girlfriend in question at the time and they had been together for 5 years. Eventually he broke up with her and we realized we had feelings for each other. We've been going out since then and things have been slow since he was just getting out of a relationship. That's the short story, and I don't care anymore if anyone I know finds this.
A couple of weeks ago I had been getting frustrated because I felt like things weren't moving forward anymore. Before I expressed this to him he broke down and told me the feelings about his breakup had just hit him and that he must've blocked out the trauma until then. We talked through everything and the main problem was that he blamed himself for everything that had happened, even though that wasn't the case. I saw his relationship fall apart by itself and told him this.
Following this talk he said he felt better about things and he started treating me the way I had been missing. I spent the night at his house and got to meet his family and everything. I told him I felt that was important to me and I was happy, and we discussed that we should still take things slow since we are both dealing with a lot of exam stress right now, but it felt like a step in the right direction. We haven't put a title on it but we agreed to be exclusive a long time ago and things feel more serious than ever.
This morning he told me he was going to his ex's cabin, just the two of them. He said they needed to talk because they're both "not in a good place". I told him I didn't think that was okay, and asked how he thought I was supposed to be okay with this. He apologized but he's going anyways. I knew they still talked sometimes which I honestly am not okay with in the first place because he doesn't tell me about it, but I was shocked when he said this. It's not that I believe he will cheat on me when he's there, it's that I don't understand how someone can have those kinds of boundaries. Yes, we have discussed this before and he knows how I feel.
Am I wrong to feel completely disrespected by this? I honestly don't even know what I'm supposed to say to him anymore, I'm just so upset. I don't understand why this is necessary and I especially don't understand why he thinks it's an appropriate thing to do.
TL;DR: my best friend/boyfriend and his ex apparently "aren't in a good place" so they're off to her cabin alone together. I feel like ****.


Source.

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