The perpetual virginity of Mary is one of four Marian dogmas professed by the Catholic Church. As a dogma, enshrined in several Catholic councils, all Catholics are required to believe it, and openly denying it is seen as heretical.
Now, the perpetual virginity myth is not true. Demonstrably so, as Matthew 1:25 expressly tells us that Joseph took Mary as his wife, and kept her a virgin until Jesus was born. We also know that Jesus had 4 brothers (Matthew 12:46; 13:55; Luke 8:19; Mark 3:31), and at least two sisters (Matthew 13:56). James, whom Paul describes as the Lord's brother (Galatians 1:19) even went on to write scripture. Jude also identifies himself as the brother of James (Jude 1:1), indicating that he also is a brother of Jesus, although as he identifies himself only as the brother of James, I am willing to let that one slide, even against tradition (Catholics take note: I put tradition in its proper place).
Now, as that is all the Bible says on the topic of Mary's sex life after the birth of Christ, that is all I am going to say about it too. Put simply, I don't care how many times Mary and Joseph did what spouses normally do. It's none of our business. It's between Mary, Joseph, and God. Now, if God had wanted us to believe the perpetual virginity, He would have at least made it possible to glean from the pages of scripture. As shown here, scripture contains all matters that concern faith and the manner of life. If any Catholic objects to that point, since Catholics believe the Church Fathers more than scripture, please note that when I said scripture contains "all matters that concern faith and the manner of life", I merely copied and pasted a translation of On Christian Doctrine, Book 2, Chapter 9, a book by Saint Augustine.
Let us therefore construct a little syllogism:
P1: If the perpetual virginity was important, it would be clear in scripture.
P2: The perpetual virginity is not in scripture.
C: The perpetual virginity is not important.
Now, as I have stated, I don't care either way. The Bible does strongly suggest that Mary was not a perpetual virgin, but at the end of the day, even if she was, that would just mean for some inexplicable reason, she permanently withheld Joseph's marital rights, in spite of the fact Paul exhorts married couples not to deprive each other, except by mutual consent, and for a time (1 Corinthians 7:5). Basically, this is such a trivial issue that I am extremely annoyed that I even have to discuss it. Why do I discuss it? Because "Holy Mother Church" has deemed that this is such an important doctrine, it would be heretical to deny it. That's right my friends, everyone who believes the verses cited above that strongly suggest Mary "knew" Joseph after they got married and Jesus was born is a heretic, so much so that if they do so vocally, they deserve excommunication.
My Catholic friends, with the greatest amount of love in my heart, I encourage you to just accept that excommunication. Or better yet, apostatise. It is a disgraceful Church that puts so much emphasis on the private life of two spouses that it constructs a whole dogma out of it. We really don't need to be discussing this issue. How many people go to Hell for believing Mary and Joseph consummated their marriage? Answer: zero. So we need not even discuss this issue. What we do need to discuss is Jesus Christ, and the salvation He brings us. Let that be our focus. Leave the mother of Christ to enjoy her eternal bliss.