I (30 F) live with my girlfriend Birdie (24 F). My girlfriend has another partner, Tiger (23 F), who doesn't live with us. Tiger's understanding of boundaries is the pop culture version, that boundaries are something you ask someone to respect rather than something to enforce.

I told Tiger if she pushed back against my "no"s again I wouldn't let her in my house. For context I said no to her helping me with something and she didn't accept that and kept pushing. It wasnt sexual but I've been abused and consent really matters to me, plus it's not the first time Tiger and I have had a consent issue. She called it an ultimatum and is upset about it.

The interaction didn't involve Birdie so i feel like it's an interpersonal issue with Tiger not something Birdie should have to fix. Both Birdie and I feel like Tiger and I should figure it out ourself but Tiger wants Birdie to take her side. Birdie is supportive of my ability to choose who comes into our house.

I can see how this looks like an ultimatum. I can see how this looks like Birdie is taking my side. Tiger doesn't read poly literature or Reddits. I don't wanna just go parallel or whatever Tiger is cool, I just can't have my "No"s ignored.

How do I explain this to someone?

I sent the boundaries vs rules article but it doesn't really explain the exact thing I'm talking about I think :T