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the biggest problem is I don't know whether or not she feels I used her
That is your biggest problem but not for the reason you think. The problem isn't that she may or may not feel used. Because even if she does, some other guy will be more than happy to crush her guts regardless of what she may be feeling in her precious little heart. Your problem is that you actually give a damn what this girl thinks.
May I remind you of what your sig line reads sir? Man up and don't worry about how some girl "feels".