One aspect of neighbourly love is that we must not merely will our neighbours good, but actually work to bring it about.
Thomas AquinasSecondly, man sins against nature when he goes against his generic nature, that is to say, his animal nature. Now, it is evident that, in accord with natural order, the union of the sexes among animals is ordered towards conception. From this it follows that every sexual intercourse that cannot lead to conception is opposed to man's animal nature.
Thomas AquinasIf, then, you are looking for the way by which you should go, take Christ, because He Himself is the way.
Thomas Aquinas