She has her own place, she's getting comfortable and used to the single life, she's may even be indulging thoughts of a relationship with someone new, she called/texted you on a friday to ask if you wanted to go out on a date and you were free and available just as she expected, you didn't play hard to get, you were easy, no mystery, you have sex, she "tags" you and she tells you after sex that "you just don't get it" and that you guys may never get back together - those aren't things people usually say after having sex.
Am I 100% correct?
No.
But I don't think that I'm that far off.
I think she is bored with what she has, she wants a challenge, she wants to chase someone, she wants someone new, and I think... you make this to easy for her.