I totally get how you're feeling. Being in a poly/BDSM relationship can be amazing, but it can also get really complicated, especially when unexpected things come up.
In my own experience, talking openly and honestly with everyone involved is key. Everyone needs to feel heard and respected...
So sorry you experienced this! I don't have any advice other to keep communicating with both parties, like you seem like you are doing. Polyamory is a learning experience for sure, so all we can do is make sure we don't keep making the same mistakes.