Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I cans see your frustration from the lack of agreement and understanding on your sexual life. For how long have you had this problem?
Are you aware of what happened in your lives-marriage by that time that could have led to this change-deterioration in your sexual life?
It is always important and necessary to know what leads to such changes otherwise you could try to make things work for you while disregarding potential issues or factors directly or indirectly affecting this area of your life.
Every person is unique and every couple is unique too. Depending on how much libido a person experiences, sexual life would be more or less active and fulfilling. We could not say that a person who has lower libido is abnormal, but we could say that couples who do not share and feel fulfilled in their concrete sexual life do not have a healthy relationship at that level.
Average would be once a week for mature couples, but again, thus drastically changes depending on each person and couple, and what makes of sexual life something healthy and fulfilling is not the mainly the frequency but how both spouses feel about it,how much both enjoy their romance and intimacy in this level.
My wife says she is tired but will stay up an hour later than me on facebook or reading a book instead of having sex she is currently reading the 3rd 50 shades of grey book so she likes readig about it but not acting it out
it seems obvious that your expectations and needs are not the same in this area, and for you to feel good and fulfilled, both need to work on it in order to get an agreement, mutual understanding and support.
Dialogue is essential, one where caring for each other needs and expectations becomes a priority for both of you.
I have tried and I am usually dismissed and she says its "normal" and no more dialogue
if dialogue does not lead to any changes or improvements, I do recommend you getting marriage counseling in order to get necessary support to develop an open , honest and proactive approach with the facilitation of an expert.
Unhappily without both of you holding accountability for the role each play in your marriage, there is no way it could improve.
Have you confronted her avoidance on this area for her to consider how much it is impacting you and your marriage?
Many times issues around sexual life in marriages do show problems in other areas, then working on this problem could lead you to improve your relationship at several levels; from communication to intimacy and empathy. When core areas like these are not working fine, the level of fulfillment in marriage is deeply undermined. Does it make sense?