Sexuality in marriage is more than just for procreation. Frequent, mutually satisfying sexual relations are a healthy part of every marriage. Don't let this confuse you about the fact that marriage is good and spiritual under all normal circumstances. Marriage is the only moral outlet for sexual passions, and sexual drive is an acceptable reason to seek a spouse. The body of one spouse belongs to the other, and vice versa.
Sexual activity is a marital duty for mutual fulfillment.
It is wrong for a person to deprive their spouse sexually except by mutual consent and only for a time. Frequent sexual activity within marriage is a good way to help one another resist temptation. If I speak in the tongues of men and of angels, but have not love, I am only a resounding gong or a clanging cymbal. If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but have not love, I am nothing. If I give all I possess to the poor and surrender my body to the flames, but have not love, I gain nothing.