I'm not sure of your sexual situation with your wife but I have been there. I'm kinda new to all this too and I'm sure that what monovchpvabcd :^) may be referring to is a post I made very similar to yours on Friday. It took my wife and I 15 years before she ever even stared to like sex with me. Of course, we had some good moments over the years but overall, pretty bad. I think she just needed to let herself feel good about herself. I'll be blunt, she started masturbating (she didn't before ... much), thought of other men during our sex, etc. It wasn't until we started really talking about all this and we began a "complete honesty" clause in our conversations did any of this ever surface.
I don't know about everyone else out there, but this openness has been the best thing ever for our sex life. She's unreal ... like a completely different person.
Hopefully, this will happen for you. Talk, talk, talk ... and don't hold anything back. I think even monogamous couples would benefit from doing this.