What should I do about my marriage?

We have been married 20 years - have 3 kids, ages 18,14,12. My wife comes from a very ually repressed Asian culture. Back when we got married I was just happy to be getting laid by this gorgeous girl - at age 23 that was enough. The thing is her aloofness - ual and in general is really taking a toll. She seems to have not one ounce of pion for me. I mean in 20 years of marriage she has never - not once - NEVER initiated with me. I am a good provider, I treat her well. I really think she gets pretty much all she needs from the relationship and thinks things are great. I have told her many times that the lack of intimacy between us is killing me, but she does not want to try any harder. I suggested marriage counseling but her response was "I can't talk to you about my issues with intimacy, why would you think I could talk to a stranger about it?" The thing is, I really DO love her, and she is a great woman and wife in pretty much every way but the intimacy. But as time goes by I find myself getting more and more resentful about her lack of pion. As my resentment builds we drift farther and farther apart. I am really really depressed about the situation. I have talked to her about this over and over but it never gets any better. I decided once to just not initiate any or affection and see how long it took for her to come to ME. Three months went by and we became basically just roommates. Eventually I went back to the same old pattern of always being the pionate one. But this is really hurting my self image. I just am really frustrated. Got any advice?