Exactly that. If she's just going to mess with your head then don't bother talking to her, at all. She'll either get bored of stringing you along and piss off, or realise she's been a fanny and come back, you either lose a bitch or get the girl you want back without her being a nobhead, win win
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You mean you were planning on going to the cinema with a girl you've never spoken to, watch a film then go home, and nothing else?! You've not really thought this through have you...