Sometimes.... well I know I do this...
When I have him at my finger tips. When he wants sex ALL THE TIME, I know I can have it whenever I want. So I don't need to WANT it, its just there for me at my liesure.
that plus
being together for a long time. Sometimes things get repetitive. Or ruetine. Which is boring and leaves you nothing to look forward too.
And when it seems he is only wanting sex, like there is nothing else he needs me for, I don't feel loved.
Add those together and I don't want sex.
Try not talking about sex AT ALL. Holding off will make her want it.
If she does something today that makes you smile, e-mail her and and leave her a comment about something she is good at that you adore about her. She will get it tomorrow and it'll make her feel really good!
Make her feel loved, beautiful (inside), and needed.
And next time you kiss her (let HER kiss YOU), do something different and a little special.