I have read the entire Catechism of the Catholic Church and there is nothing in it which says that it is a mortal sin to refuse to have intercourse with one’s spouse or that one may refuse intercourse only for a serious reason. That is not to say that spouses do not have a right to intercourse because they do, but I think this priest’s opinion is extreme.
He's an 'orthodox' priest ;-)
1 Corinthians 7
3Let the husband render unto the wife due benevolence: and likewise also the wife unto the husband.
4The wife hath not power of her own body, but the husband: and likewise also the husband hath not power of his own body, but the wife.
5Defraud 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.