Where does the Church teach the person who least desires sex gets to determine the frequency of marital relations? That would be rather selfish on the part of the person who is not interested in having relations. Remember love is selfless, not selfish. One partner does not have veto power over the other. Marriage is about the mutual gift of self.
When a couple marries, they do give each other rights to the marital act:
Discussing the object of consent, St. Thomas observes that the spouses explicitly "consent to marriage and implicitly to the mutual yielding of the right over the acts proper to marriage."8 Surrendering to another person the right over one’s acts means giving one’s will over those acts, and since free will means also possession of self, by giving one’s free will over certain acts, the person gives his or her self. The spouses consent to give to each other the right to certain acts or services ordered to the ends of marriage, and through the mutual, exclusive, perpetual and irrevocable right to these very personal acts,9 they mutually give and accept each other in order to form a marriage. This is the object of marriage consent which, in juridical terms, can be formulated as the ius ad operationes coniugales. It is important to understand that the ends of marriage (“the good of the spouses and the procreation and education of children”) cannot be the direct object of a contractual agreement because the attainment of those ends is not always within the spouses’ power. A marriage is valid as long as the spouses consent to the acts ordered to those ends even though the good of the spouses, the procreation of offspring or the upbringing of children may not be successfully attained.
catholic.net/rcc/Periodicals/Homiletic/06-96/2/2.html
I’m not saying it is all about the needs of the partner that wants more frequent relations. I am just saying that the needs of the individual who is disinterested do not outweigh the needs of the spouse who is interested.
And of course the disinterested spouse is gravely sinning against their marriage if they are holding marital relations at ransom, to have power over their spouse in some other avenue.