I agree with what everyone's said here, but I have to say that given the circumstances I'd be most likely to go with what Lixy said.

You must remember that at 19, your girlfriend may not have learnt to be as honest about your sex life as she may make out (speaking from experience here) and she may now be worrying about how wet she is more than she's thinking about sex.

I would recommend that you at least try getting her as turned on as possible (rather than just 'turned on enough'). Double the length of time you spend on foreplay and don't penetrate her until she's literally begging for you to do so. Even if it turns out that the dryness has nothing to do with how turned on she is, no woman is going to complain about this sort of treatment.

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