If there's one thing that bothers me about women, that's it.... She has a bf and yet at the same time feels like she has a right to complain or comment about whatever girl your seeing with, talking to, or even just having fun with. My ex a few weeks back told me she was hurt by me talking to my previous ex and i'm like wtf you have a bf I can talk to whomever I please...
Anyways back on topic... that last little line she used is classic. If you haven't really been talking or paying attention to her she fears that you are starting to get emotioinally detached. And that last line she threw in there sparked an emotional response out of you, even if it's a bad one it tugged at your emotions which is exactly what she wanted. Don't buy into it. Don't even make excuses about who you are talking to or what you're doing. Let her know that she didn't want you anymore she wants the other dude so that immediately means that she has no say and that you won't be waiting around for her to come back. Yes I know that won't be true since you stiill have feelings for her, but regardless you can't let her know that.
Be careful with your heart, because when someone seems too good to be true, they usually are.