The title is abominable enough, but it is in fact true: i know some novus ordos who believe such a thing.
This is what this pathetic Vatican 2 sect has come down to: you have supposed would-be "Catholics" who believe St. Joseph was an adulterer. I don't know how many in the area believe it, but i know that a couple who is "in charge" of the "Family Pastoral" of a substantial area or "Pastoral Family" or whatever its name is, do believe in it. There may be more.
They picked it up from a publicly sodomite and effeminate presbyter who preached such a thing in an actual novus ordo mess. Yes!
What would such a thing be? Blasphemy? Heresy?
It goes without saying that you can deduce that such a wicked idea is utterly false just from the fact that St. Joseph was the holy foster father of Our Lord! And from the fact that the Blessed Virgin Mary was and is and ever will be a Holy Virgin, and that she was married to St. Joseph who was obviously holy his entire life!
Those two things should be more than enough, but you know how novus ordos are. So, is there any specific definition from the Church or something else anywhere that says that St. Joseph remained a virgin until his death?