She is probably going through the menopause, and that will affect her libido, as well as her lubrication. But she does still have sexual needs, and ultimately sexual intercourse is the bonding activity so important for marriage. However, there are ways to accommodate this. Both spouses have an equal responsibility to satisfy the other's sexual needs. It may be that in the past you have not paid enough attention to her needs, and she has had to make do with what she gets in response to satisfying you. If so, then you need to recognise that, apologise for it, and discuss how to meet her needs. Find out exactly why, non-confrontationally, she brushes you off. Listen carefully, acceptingly, lovingly without arguing. The biblical term used in "he knew is wife" is more than a euphemism for copulation. Your wife is an individual with changing needs; not just a text-book female body. Then let her know your needs, and discuss how they can be met. You say you need sex twice a week at least, so how was that met over the years, and how has the need been met over the last 6 months. I hope this helps as a start.