Hi,
We answer this one over and over. You are assuming that the word ‘until’ can be used in only one way as in: “He was faithful to her until she went on vacation.” Here it is possible that he was unfaithful to her while she was away. ‘Until’ means up to a point and following. This is how you assume the Scripture passage is using ‘until’. However, the word can be used in another way as in: “He took care of her until she died.” Now, he couldn’t take care of her after she died. Here ‘until’ mean up to a point and not after. This is the way it is used regarding Mary’s perpetual virginity.
Fr. Vincent Serpa, O.P.