Martin Luther was once also a Catholic priest in a Catholic church; and he, too, led many astray, as your "teacher" has done you. But I don't think Luther ever formerly denied the perpetual virginity of the Blessed Mother, as you and your "Catholic priest" teacher do.
How about that? Martin Luther appears to be more Catholic than some people who still claim they're Catholics!
How about simply reading the Bible, instead of reading things into the Bible? The Bible clearly states that Mary was married to Joseph. The Bible clearly states that Jesus had brothers and sisters. Why is it therefore wrong to conclude that Joseph and Mary enjoyed a happy normal marriage and that Jesus had brothers and sisters? We have no problem believing that Adam and Eve consummated their marriage. Why do we doubt that Mary and Joseph consummated their marriage? The Lord commands us to be fruitful and multiply after all. Physical intimacy between a husband and a wife is a precious gift from God.