Well, I really think she's being a bit of an idiot, myself.

You were straight up and told her you weren't looking for a relationship or anything, and she acknowledged that and still slept with you. If she was really cool with this, she would've kept it friendly and left it at that. However, it seems to me that she was playing on that dumb female fallacy of "If I sleep with him maybe he will like me!". Duh. Why do girls not get this?

So your lack of attention showed her that her theory was wrong and she probably felt rejected and embarrassed. Stupid, though really. It's not like you led her to believe you were interested in her. So it's all self-inflicted. You shouldn't feel guilty or used, you just took what was offered. If she chose to play mind games with you over it, that's her issue and not yours.

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Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi