I’m the product of a mixed marriage, and somewhat confused about Catholicism vs. Protestantism. I have a Protestant girlfriend and after much discussion, it looks like the only way we could be together is for me to convert. The CCC seems to indicate that if I do so, I would be damned forever, unless I return to the Catholic church before I die. I have to know if that is really true.
As a Catholic you believe that the Catholic Church is the only Church founded by Jesus Christ. While still believing this, you are asking if joining another church is acceptable. You already know the answer. No one is worth giving up the greatest gift you have! No one is worth mortal sin.
The Catechism of the Catholic Church is simply calling it as it is. You are in my prayers.
Fr. Vincent Serpa, O.P.