I dunno MooseMan, I'd almost prefer the honesty of the last sentence you wrote,

since I loooooooove it when my bf unapologetically states that he is dying to fuck me. Not to say that I don't swoon over genuine erotic language, but your earlier sentences sorta make me smile more than get turned on...

(no offense, since it sounds like you already know they're a little over the top).
But yeah, I agree that there is a fine line between erotic and pornographic... virgin, in your "lick her cunt..." etc statements, the focus seems to be on you. This isn't bad; believe me, she WANTS to know how badly you want to fuck her and no one else, how you've been thinking about nothing else since she's been gone. That will turn her on. But focus on how SHE would feel in response to your body, and communicate your sheer lust to her and try to anticipate her needs while reading the letter. She'll long for you to
say certain things, just as with sex she longs for you to
touch certain parts of her. And if she's your wife, I'm sure by now you know what those things are!! Hit all the right verbal buttons, man!
