I am sorry that was your experience. The defining document is the Catechism, and it speaks clearly.
It is certainly your choice to believe as you wish, but if the priest said what he said, he was in error.
St. Bede (d. 735) refutes both of the things the priest said, at Mark 3: 31-36.
The Bible, as written, was in several different original languages. It wasn’t until St. Jerome translated the books of the Bible into Latin. From there, we read the Bible in our own language. Without context, any number of interpretations arise. Without the teaching authority of Church, these incorrect interpretations give rise to false doctrines. As mentioned above, false statements about the perpetual virginity of Mary existed in the 7th and 8th century.
It may be worth your time to read this book (http://www.ewtnreligiouscatalogue.com/Home+Page/BOOKS/Bible+Study/DOES+THE+BIBLE+REALLY+SAY+THAT.axd) and find a good study Bible.
The Catholic Church has been teaching the fullness of Christian faith since the beginning. Any question you may have has likely been asked in the 2000 years since the Resurrection. I encourage to ask them! Ask your pastor. Also, consider reading catholic.com and ewtn.com.
It is certainly your choice to believe as you wish, but if the priest said what he said, he was in error.
Just sounds like an honest priest to me and does not mean that he believed Mary had other children but only that Jesus had brothers and sisters, not the same thing.