Is the wife required to ask her husband for sexual intimacy, and is she considered negligent or sinful if her husband abstains from her?

A wife is obligated to answer her husband's call to bed unless she has a valid excuse, but she is not obligated to offer herself to him. As long as you do not refuse to obey your husband in matters of intimacy, there is no blame upon you. Your husband has no right to abandon you for the reason mentioned. Rather, it is his duty to keep you chaste to the best of his ability and according to your needs.