This is a common subject here… no worries!
First… NFP is not “birth control” because you aren’t simply having sex whenever you feel like it and controlling your fertility at the same time…
NFP is making the choice to abstain at certain times if you, as a couple, feel it is necessary.
The debate that will often come up is “when is it necessary”…
The catechism says…
A particular aspect of this responsibility concerns the regulation of procreation. For just reasons, spouses may wish to space the births of their children. It is their duty to make certain that their desire is not motivated by selfishness but is in conformity with the generosity appropriate to responsible parenthood. Moreover, they should conform their behavior to the objective criteria of morality:
When it is a question of harmonizing married love with the responsible transmission of life, the morality of the behavior does not depend on sincere intention and evaluation of motives alone; but it must be determined by objective criteria, criteria drawn from the nature of the person and his acts, criteria that respect the total meaning of mutual self-giving and human procreation in the context of true love; this is possible only if the virtue of married chastity is practiced with sincerity of heart.156
"By safeguarding both these essential aspects, the unitive and the procreative, the conjugal act preserves in its fullness the sense of true mutual love and its orientation toward man’s exalted vocation to parenthood."157
Periodic continence, that is, the methods of birth regulation based on self-observation and the use of infertile periods, is in conformity with the objective criteria of morality.158 These methods respect the bodies of the spouses, encourage tenderness between them, and favor the education of an authentic freedom. In contrast, “every action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible” is intrinsically evil:159
Thus the innate LANGUAGE that expresses the total reciprocal self-giving of husband and wife is overlaid, through contraception, by an objectively contradictory LANGUAGE, namely, that of not giving oneself totally to the other. This leads not only to a positive refusal to be open to life but also to a falsification of the inner truth of conjugal love, which is called upon to give itself in personal totality. . . . The difference, both anthropological and moral, between contraception and recourse to the rhythm of the cycle . . . involves in the final analysis two irreconcilable concepts of the human person and of human sexuality.160
Many will try to argue exactly what those JUST reasons are. That is between you, your spouse, and God alone.
I hope that helps a little…
NFP is a totally allowable technique to use as faithful Catholics… don’t ever worry about that! The fact that you’re using NFP means you’re being “open to life”… open to God’s will in your life…