It is hard to find equivalents between a sexual and emotional relationship. So for me, I have found myself justifying friendships where the other person is a shit to their romantic partner, but awesome to me. I think, well, they won't do that to me!

But they will. It is just that a sexual relationship involves a different sort of betrayal. Cheating is pretty easy if you have access to penis whenever you want and you can justify it as "well, there were problems but we worked on them so no need to bring it up."

But she has that dishonest streak and will do something to you the moment it suits her. So it is best to realize deep down she justifies lying and hurting other people. The moment that clicks, it will be easy to call her boyfriend and tell him.

I would be careful though, if she has dirt on you then it will likely come out. Make sure you have any property back that you loaned her and that it is going to be a clean break. Because the moment you ruin her relationship, you friendship is over.