The "until" with Michal was a point in time that happened to be her death. It could have been any point in time. With a similar intepretation, Michal had children after her death. Again, the sentence says ZERO about after the point time. You keep trying to create a starting point closer to your conclusion, this time you say "leaving open the possibility." According to your logic, the Michal sentence leaves open the possibility that she had children after she died. In fact it says NOTHING about what happened after the point in time.
Indeed, there is no "proof" in the Bible that God is one God, three Persons. Nothing explicit. Yet you don't require it be so because you believe it as a matter of faith just as I do. You're Bible-only-must-be-explicit for Catholic doctrine that you don't believe.
Usage: The Greek word "ἕως" (heós) is primarily used as a conjunction or preposition to denote a point in time or space. It is often translated as "until" or "till" when referring to time, and "as far as" or "up to" when referring to space. In the New Testament,
it frequently marks the end of a period or the extent of an action or event.
11 Whatever town or village you enter, search there for some worthy person and stay at their house
until you leave. (Matthew 10:11)
Implied is that you will no longer be staying at their house after you leave.
29 “‘No,’ he answered, ‘because while you are pulling the weeds, you may uproot the wheat with them. 30 Let both grow together
until the harvest. At that time I will tell the harvesters: First collect the weeds and tie them in bundles to be burned; then gather the wheat and bring it into my barn.’” (Matthew 13:29-30)
Implied and stated that he would separate the weeds from the wheat after the harvest.
28 “Truly I tell you, some who are standing here will not taste death
before they see the Son of Man coming in his kingdom.” (Matthew 16:28)
Implied is that they will see the Son of Man coming in his kingdom.
These are all the same word as in Matthew 1:35. In each case, there is an implied or stated change after the "until." If Matthew wanted to teach the perpetual virginity of Mary, he could have simply said, "Joseph kept her a virgin." He added "until" because his action of keeping her a virgin was "until" she gave birth. Otherwise, there would have been no need to add "until." Grammatically, the Greek word does not require an action after, but the context is what tells us and I think (my opinion) the context of Matthew 1:35 is that they did not have relations until after Jesus was born but did later once married. If you want to argue that I can't prove that, then admit that you can't prove they didn't.
This source says the action (keeping her a virgin) terminates after the condition is met (Mary giving birth).
I agree you can't prove from that verse alone that Mary lost her virginity after the birth of Jesus, but neither can you disprove it. The Catholic insistence that she remained a virgin for life comes from an extra-biblical belief that we have no record of being taught before the 4th century. If you want to believe that and believe all the references to His brothers and siblings are cousins, then be my guest. I think the most natural and plausible reading is that she did. My salvation does not depend on whether or not Mary had other children. To Catholics, it is taken as an insult to suggest Mary had other children and was not a perpetual virgin. Some Catholics have even gone so far as to argue she felt no pain in childbirth and her hymen was never broken when birthing Jesus. Yes, God could have miraculously enabled Jesus to be born without breaking Mary's hymen, but I see no reason to believe that, and I don't see the reason some argue for it. So what if her hymen was broken? That would not prove she had sex. It can break for other reasons, like birthing a child (and they believe she got pregnant by the Holy Spirit), so why argue for an unbroken hymen? It seems like another attempt to argue Mary was a virgin in everyway possible when Scripture does not demand that.