This is not what most Catholics want to hear. But it is true, and it is crucial to avoid grave sin, so I will say it again and again.
YOU CANNOT HAVE A MARRIAGE THAT IS PLEASING TO GOD, UNLESS YOU UNDERSTAND RIGHT FROM WRONG.
Are you Catholic in belief and practice, or in name only? If in belief and practice, then tell me, what does the Magisterium teach on the basic principles of morality? Do you understand, and can you explain in your own words, about the three fonts of morality, intrinsic evil, and the moral object? The vast majority of Catholic spouses have never heard of the three fonts of morality. They have no idea what makes an act intrinsically evil. They do not know what a moral object is, nor why an evil moral object makes an act intrinsically evil and therefore always a sin to knowingly choose.
But more importantly, most Catholic spouses are unable to apply the teachings of the Magisterium on the basic principles of ethics to their own lives, in such a way as to decide which acts to commit and which to avoid. In the realm of sexual ethics, most Catholic spouses know that certain kinds of acts are prohibited by the Church, such as abortion, contraception, premarital sex, and adultery, but they do not truly understand why. And the same is true for intrinsically evil sexual acts within marriage. They have heard that certain acts are prohibited, or they have heard, incorrectly, that certain acts are permitted. But they lack a sufficient understanding of the basic principles of ethics in order to distinguish true from false claims about marital sexual ethics. They lack a sufficient understanding of morality to realize why one act is gravely immoral and another act is morally permissible. As a result, they are easy prey for false teachers.
If you are Catholic in belief and practice, how can you believe the teachings of the Magisterium on ethics if you have not learned the basic principles? And how can you practice the teachings of the Catholic Faith on ethics if you do not know what to believe? Correct practice is based on correct belief. So in order to live the Catholic Faith, you must know what to believe. Neither is it sufficient for you to merely look up each and every particular act in a book, to find out if that act is moral or not. In order to apply the ethical teachings of the Church to the complex circumstances of your life, you must understand the basic principles.
Without a good understanding of the basic principles of ethics, Catholic spouses will not be able to oppose the pornification of their own marriage by the influence of secular culture and false teachers. So the second remedy is to learn the teachings of the Magisterium on the basic principles of ethics. These teachings are not theological opinions, but required beliefs. The Church has definitive teachings on the basic principles of morality, as well as definitive teachings on particular types of acts.
The above text is an excerpt from my book:
Roman Catholic Marital Sexual Ethics