[Titanites]

Scripture is very clear here that married men and women are not to with hold sex from one another.

Yes, that is true. If a spouse requests sex and the other refuses on a regular basis, that is a sin. But that does not apply to the situation where both spouses mutally agree to not have sex, which is not a sin.

[Full Court]

But that does not apply to the situation where both spouses mutally agree to not have sex

1 Corinthians 7:5
 Defraud ye not one the other, except it be with consent
for a time,
that ye may give yourselves to fasting and prayer;
and come together again,
that Satan tempt you not for your incontinency.

James 4:17  Therefore to him that knoweth to do good, and doeth it not, to him it is sin.

And Mary was not the Ark of the New Covenant. Jesus is the mediator of the New Covenant.