It would be a deal breaker for me too- if you're not having sex at all - that's more like a relationship between siblings than marital partners. Maybe you could explain it to her like that - that you feel as if you may as well be living with your sister - someone you love but are not initimate with.
And Hawkeye's right - if she's not feeling it at this point in her life, at 38- when most women pretty much come into their own sexually (although I know everyone's different and I hate to generalize) - she probably just won't feel the need at all - especially if she's not shown any indication of being interested in the last four years. Does she not even show any sort of sign of responsibility about it - as in - 'I married this poor guy - I should give him SOMETHING....' (you know 'wifely duties)

. I'm kind of kidding - but fair's fair.
Although that's one thing I don't understand...and it's been a pretty constantly running theme that I see over and over on this forum- how do people decide to marry people with whom they have no sexual chemistry or compatibility? I just don't get that. To me that would have been a deal breaker before it even got to the point of having the question of marriage or even the next date arise.
Because if you don't have the desire to have sex with someone - isn't that a pretty good indication they're not the one for you? And if they don't seem to want to have sex with you - shouldn't that set off some sort of alarm?
I don't know - in my experience- when the desire's there - it's not a question of whether or not - it's something that seems like it has to happen - inevitable - like breathing.
If that feeling wasn't there for me - I'd have taken that as a sign- not the one.
You don't want to spend your whole life feeling unwanted and she probably doesn't want to spend her whole life feeling like she's failing you or being asked to do something she apparently has no desire to.