It sounds like your ex is far more confused than you should be. My main concern is that you might be being manipulated in order to fulfill someone else's need(s).
The other thing to consider is the current boyfriend. No matter what might be going wrong in that relationship it's not right or fair to that man to carry on while it's still a 'relationship'. How would you feel if she lined someone else up while you were still with her? Or nude pics?
Whether she's feeling insecure, bored or lonely it really doesn't matter. Her behavior isn't respectful to her boyfriend, to you or to herself. She isn't respecting the relationship she's in; she isn't respecting your feelings and chances are that if she gets what she wants you're going to get hurt (again)
Take that step back and look at this whole picture; the situation from a wider viewpoint.
You're sharp - or you wouldn't be confused about this. You just need to hear that someone else is seeing what you think you are (seeing).
If you want to continue talking to her, it will be difficult, but you have to keep that point of view. And always, always ask yourself: If she's doing this to her boyfriend, why wouldn't she do it to you?
Until she asks for help and follows thru with getting it, this is who she is.
Nothing confusing about that is there? Trust your instincts