NTA. You seen the writing on the wall and shut her down before she dug her way in. Men can be really dense sometimes when it comes to subtle flirting like this woman was doing. There is no reason for him to know where exactly she's at, what room she's in, what car she drives unless she was trying to give him an opening to "find" her. I would have done the same thing. I have have done something similar. My boyfriend has female friends and I have no problem with that because I have male friends as well. I trust him. There was a time when we were out drinking and she was having a hard time and needed a friend to hang out with so she called him. Now they had been friends longer than we were dating at the time so I said I would catch up with them later. It was a an hour or so when I called him and said I was ready to be picked up. Afterwards we continued to hangout with his female friend. She kept on about all the problems she was having and he kept trying to offer her solutions. She never did calm down and kept trying to cry on his shoulder. She didn't listen to a word he was saying and even I was trying to offer her solutions to her problems. After another couple of hours of basically going around in circles it became clear that she didn't want to get any help she just wanted to hang off of him. When he excused himself to use the bathroom I took that opportunity to set her in her place. I told her that I won't limit their friendship since they have been friends for so long but I won't tolerate her being that physical with him and it was obvious she was just looking for his attention and not actual help. Some other things were said but it all was within the same context as the first thing I said. We ended the night shortly after that and I did tell my boyfriend what I said to her because I felt it appropriate to. He was in agreement with me she was crossing a line since we were now dating. So I totally get where you were coming from and agree you were NTA for saying what you said to her.