I have to agree with the others who say...your W knows darned well that she wasn't fulfilling the Monday night agreement. True, perhaps "sex" doesn't have to happen every Monday night...but the point behind scheduling time for the two of you is to form "intimacy" in some manner. Sitting in separate chairs reading a book....is basically ignoring the other persons presence...she was in her own little world by doing that and she knows it. You cannot form intimacy with her while she's wrapped in in the plot of a book.
I agree...this needs to be brought up at your next MC session, you need to say how you feel about all of this in that session too....no holds barred honesty.