With respect, Livindesert, perhaps you should not be so quick to dismiss the evidence from the Gospel of Luke. You have been polite and asking honest questions that deserve an answer.
Part of the issue here is that you seem to want some sort of explicit specific reference to Mary's supposed virginity (at least when it comes to what is found in the Bible), or else the Tradition itself is naturally suspect. Actually, it is a wise, good, and healthy thing to be suspicious of traditions that do not fall within your own traditional understand of Scripture - so I am not criticizing you in any way for that.
But are there not numerous examples (and I can list some if you want) of Scripture hinting at things but not explicitly stating them? And don't Christians - of all types - struggle to grasp deeper meanings that fall within traditional Christian interpretation? For one of many examples, do Christians reject the Arian (and modern-day JW) interpretation of "The Father is greater than I"? To Arians and JWs this is supposed to mean that Jesus is not Divine, but rather something less. But that interpretation does not fall within the Traditional understanding of this very mysterious thing that Jesus said. We need to delve deeper and reflect on what its possible meaning(s) might be.
So, in a similar way, we need to not only reflect on what is explitictly said in Luke between Mary and Gabriel - but also what is assumed.
As we already know, Gabriel is explicit and specific when he tells Mary that she will (FUTURE tense) bear the Son of the Most High.
And what is her response?
She asks a very profound and meaningful question that works on more than one level. She asks, "How shall this be, since I have no husband?"
At first glance, this seems to be a reasonable question. At the time, she was a virgin - and therefore it would not make sense to claim that she would conceive right then and there. But Gabriel had used the future tense.
So...while she did not yet have a husband at that time...she was betrothed - and she knew she was going to soon be married. And that makes a big difference in how we are to read her response.
For if you or I would approach a young woman - a virgin - who is engaged to be married and said, "I had a vision that you will have a son" - would she ask the same question that Mary asked? No. She would assume that after her wedding day she and her husband would join in marital relations and someday have a child.
The question Mary asked only makes sense if she intended to never have sexual relations with her soon-to-be future husband.
Her question only makes sense if a vow of chastity was already assumed. In our make believe scenario a bride-to-be would never be baffled at the thought that one day she would conceive. But Mary was. Think about it and reflect upon the deeper meaning here.
It is only after Mary asks this question that she is told - explicitly - how it is that she would conceive even without ever engaging in a sexual act.
Of course, the Gospel of Luke was not written to be a medical textbook, nor did it delve into questions like Mary's sex life. But still, within the text, there are hints and deeper meanings that tell us there might be good reason to see why the Church has Traditionally viewed her as being a perpetual virgin.
For an excellent short article shedding more light on this topic - using the Book of Numbers as its focus - see this link:
The Sacred Page: A Biblical Basis For Mary's Perpetual Virginity?
God's Peace,
NewMan
