I just wrote a good reply to this in a very similar thread last week.
Required reading:
$M on Ownership
http://www.pua-zone.com/showthread.php? ... #post27844
Original post he references
http://www.pua-zone.com/showthread.php? ... rtance-of-
Now, seriously.. to help you we need to know a LOT more information. The main question on our minds is.. is it because the sex is bad / boring? This is all on you. As the guy, you are required to initiate sex, be good enough to give her orgasms, and provide as much variety as possible (toys, positions, speed, types of orgasms, light bondage, etc). How long do you typically last? How is the foreplay.. do you go down on her before you have sex? Are you dominant in bed? Do you talk dirty to her during sex?
You see what I'm getting at here?
Second, what are her fantasies? Have you created a non-judgmental environment where she'd feel comfortable telling you about her vampire cos-play play-rape fantasy (etc)? Are you helping fulfill those fantasies? This is where the good communication comes in. Don't talk about the problems.. talk about preferences and turn-ons. She's not going to volunteer this stuff.. you need to get her to open up about it.
Lastly, are there any other possible contributing factors we should know about? For example, are either of you stressed out, prone to depression, or just unwell in any way? Oh, and this is important, how often do you see each other? How often do you text / talk on the phone on a daily basis?
-Wolf
It's essentially the same thing Chefguy is talking about. You should read the whole thread:
Here's another link to a post my girlfriend wrote about why guys nearly all suck in bed:
I don't necessarily advocate getting relationship advice from women, but my girlfriend is a playette and she knows what she's talking about.
Hopefully, some of that is helpful. At the very least, read the first link. $M probably addresses the issue way better than I ever could.