You went too soft, too, too fast; which is indicated by the lack of interest she has shown you. She obviously likes some element of the 'bad boy.' If I were you I'd tell her that you need to talk when she gets back. Leave it at that. Hopefully this will regain her interest, and soften the damage that the sappy letter did. When she gets back, then you can properly talk about where you two are at.

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It's like in the Seinfeld episode where...