I am sure this is familiar to you:
V. THE GOODS AND REQUIREMENTS OF CONJUGAL LOVE 1643 "Conjugal love involves a totality, in which all the elements of the person enter - appeal of the body and instinct, power of feeling and affectivity, aspiration of the spirit and of will. It aims at a deeply personal unity, a unity that, beyond union in one flesh, leads to forming one heart and soul; it demands indissolubility and faithfulness in definitive mutual giving; and it is open to fertility. In a word it is a question of the normal characteristics of all natural conjugal love, but with a new significance which not only purifies and strengthens them, but raises them to the extent of making them the expression of specifically Christian values."152( http://www.vatican.va/archive/ccc_css/archive/catechism/p2s2c3a7.htm)
No where is there any Gospel that suggests that Mary ever had sex.
Well as I indicated in an earlier post, we do have the 'till' or 'until' to consider. Striking because Matthew is being quite clear Joseph DID NOT touch Mary in any 'conjugal' way 'till' Jesus Christ was born. None of the NT writers get into the conjugal actions of Mary and Joseph but leave us with 'till' and 'until' to make it clear she was truly a virgin 'till' the birth of Christ.
That's what we have to operate with. That's all the 'till' or 'until' which should be clear enough. Then we have the accounts of brothers and sisters in the Gospels. One can say cousin or kin all they want but the Greek has words for that too and those words were not used. We could argue all day, cousin, brother, sister, etc. but the 'till'/'until' is pretty clear throughout Matthews Gospel. It literally means UNTIL.
ANd the question remains. Jus tWHY is it so important to Catholics taht Mary be perpetually virgin?
The prophecy about her was that a virgin would conceive and bear a son.
That happened and is still valid even though she did not remain a virgin perpetually.
The other issue is the whole Catholic mentality about sex. They way they exalt virginity and chastity as preferable when even God said that it was not good for man to be alone, shows there is some kind of warped thinking about sex that is not Scriptural.