Folks, this is Traditional Theology, not General Theology. We welcome everyone who posts here, but please read the Statement of Purpose regarding what this forum is set up for.
Traditionally, the Church DID teach that Mary remained a virgin, as there were some doubts that arose among some within the first few centuries. There are a number of reasons this was held as belief, not only the Protoevangelium of James. Even those who put little stock in the PoJ recognize Mary as a perpetual virgin.
There are answers to each of the particular quotes from Scripture that modern denominations assume mean otherwise and we can talk about each of them. (No time at the moment - I think most everyone who posts here is in Church and I need to be soon.)
Mary was regarded as a lifelong virgin by essentially all Christians until just a few centuries ago when it was assumed against Catholicism and Marian devotion - which Orthodox would agree was excessive at times in their case, yet we don't change what was always believed to counter it.
But if you are not a Traditional Christian (see the SOP for a definition), please don't post debate and your own opinion, because those are against the rules for TT (see the SOP) and I don't want to see folks get in trouble.
I'm sure we can answer more in depth later today.
God be with us all.