First of all, although you ask for scripture only in this matter, Catholics don’t base all their beliefs in scripture only. Keep in mind that scripture can be vague and that is why we turn to the Church, which was founded by Christ (therefore it was around when Mary was around) for information. However, I will try to address the “until” issue. The word “until” as used in scripture does not necessarily mean the same thing as it does today. In other words, “until” often means “up until the time” without implying that an even occurred after. Here are some examples given by
www.scripturecatholic.com :
Matt. 1:25 - this verse says Joseph knew her “not until (“heos”, in Greek)” she bore a son. Some Protestants argue that this proves Joseph had relations with Mary after she bore a son. This is an erroneous reading of the text because “not until” does not mean “did not…until after.” “Heos” references the past,
never the future. Instead, “not until” she bore a son means “not up to the point that” she bore a son. This confirms that Mary was a virgin when she bore Jesus. Here are other texts that prove “not until” means “not up to the point that”:
Matt. 28:29 - I am with you “until the end of the world.” This does not mean Jesus is not with us after the end of the world.
Luke 1:80 - John was in the desert “up to the point of his manifestation to Israel.” Not John “was in the desert until after” his manifestation.
Luke 2:37 - Anna was a widow “up to the point that” she was eighty-four years old. She was not a widow after eighty-four years old.
Luke 20:43 - Jesus says, “take your seat at my hand until I have made your enemies your footstool.” Jesus is not going to require the apostles to sit at His left hand after their enemies are their footstool.
1 Tim. 4:13 - “up to the point that I come,” attend to teaching and preaching. It does not mean do nothing “until after” I come.
Gen. 8:7 - the raven flew back and forth “up to the point that” [until] the waters dried from the earth. The raven did not start flying after the waters dried.
Gen. 28:15 - the Lord won’t leave Jacob “up to the point that” he does His promise. This does not mean the Lord will leave Jacob afterward.
Deut. 34:6 - but “up to the point of today” no one knows Moses’ burial place. This does not mean that “they did not know place until today.”
2 Sam. 6:23 - Saul’s daughter Micah was childless “up to the point” [until] her death. She was not with child after her death.
1 Macc. 5:54 - not one was slain “up to the point that” they returned in peace. They were not slain after they returned in peace.
In other words, the whole point of the word until in this passage is not to say that Mary and Joseph had relations after the birth of Jesus. It doesn’t have anything to do with that. Rather, it is reaffirming that Jesus was born of a virgin as prophesied.
Hope this helps.