I feel for you. I have been there for 2 years with me doing that to my husband, unintentionally. I just didn't think sex was that important in a marriage. My turnaround came when he told me that the lack of sex would easily drive him to cheating on me and that had been masturbating for approximately 6 months. It hurt me so bad to know that I was sleeping in the same bed as this amn and failing to meet his one need that I should be fufilling.

I have a few suggestions to try help:
> talk to her outside the home environment e.g. when taking a drive somewhere. She will become defensive but tell her you aren't judging her but letting her know what the lack of sex is doing to you. After such a conversation take more walks, just the 2 of you. Try and be touchy touchy with her and focus the conversation on finding out more about her sexually. Create a conjusive environment for her to open up to you (meaning you do not accuse or judge her (difficult to do with arguing!!) good luck1
> make sex dates and have spontenous sex e.g. when takinging a long drive with her driving and suggest along the way that you have a quickie
> take her out for a day or overnight to a place with no technology except for runningwater and electricity and focus on each other
> help out around the house or with whatever maybe causing her not to want to be with you
> ask her about any fantacies she may have and then later try create them as a suprise
> make her feel sexy
> create a longing for sex in her e.g. on th first day kiss her only; day 2 - kiss and light touchig with hands only; day 3 full body touch (be creative); day 4 all the way. on the 1st or 2nd day she maybe confused why you seem to just leave her hanging. Hopefully you can create some anxiousness or curiousity for the next day. You can make the days as long as you want.

hope something helps