Other way around - you're right I left these details out, didn't seem pertinent. I'll explain a bit.

Just after they started dating, I agreed to let the boyfriend move in with me. K said she would side with me if there were ever any problems.

There were problems almost immediately, he barely paid any rent for the first three months. Rather than siding with me, K allowed the boyfriend to move in with her for free.

To both of their credit, he did pay me back eventually. It just took a lot of reminding, a lot of him guilt tripping me, and 10 months.