I’m sorry, but this whole thing is ridiculous for a couple of 40-somethings.
You called her your girlfriend but also say you weren’t committed. You ended whatever kind of relationship you did have because she saw something old on FB and called you to freak out about it at 5:30 a.m., at which point you called her a stalker and told her to butt out of your life. So you stopped talking and she went on vacation. You got upset that she was flirting on vacation even though you weren’t together anymore by your own doing.
You weren’t together when she was on vacation, so what she did was her business. I can understand having a fling on vacation, but what on earth is there to “end” with a person you meet on a four-day vacation?
I still think you two sound like too much drama.