I’m going to be the curmudgeon here, or should I say, the realist.
You shouldn’t be dating her and you certainly shouldn’t be marrying her.
Marriage is becoming one. When you marry someone of a different religious faith, you will not become one, you will become 9/10. That’s not one.
There will always be that part of your life that is closed off to her, and that part of her life that is closed off to you. You may be cool with it now, but It is unbelievably and incredibly sad in real life. You simply cannot share EVERYTHING with your wife and she cannot share EVERYTHING with you. It can never, ever be “complete.”
Chances are good that she will prevail when it comes to raising children because she is the one who will probably be spending the most time with the children (unless you are planning to be a stay-at-home dad and she will be working outside the home). Chances are very good that you will discover over the years that you are doing more and more non-Catholic activities for the sake of the children, and eventually, you will abandon the Catholic Church altogether. Protestant churches are lots of fun, and provide many support systems that Catholic churches do not have. It’s really easy to lose sight of Jesus in the Blessed Sacrament when you are faced with the exciting opportunities in the Protestant churches. The music alone is enough to lure many Catholics away from their parishes. You may think you are different and “stronger”, but many have thought the same and now they sit in Protestant churches.
That is, IF the two of you stay married. You and she have a totally different perspective on religion. There is a good chance that you will discover how much your childhood religion and upbringings have influenced many other aspects of your life, too. One good example is artificial birth control. Another is masturbation. A third example is sexual stimulation between couples leading to orgasm but not intercourse (heavy petting, oral sex, anal sex, etc.) Most Protestant churches teach that these practices are perfectly acceptable.
Those are just a few examples. There are others that are not sexual, e.g., differing views on drinking alcohol, spending money, politics, socializing, etc.
I would say leave now. There are plenty of Catholic women available who would love to meet you and be a good, Catholic wife to you and mother to your children.
You don’t have to be mean or cruel about it. It would be meaner and crueler to prevent this girl from finding a good Protestant man to marry and have children with. Think of it this way–you are also depriving her of a complete marriage.
Don’t settle for 9/10 of a marriage and if you love her, don’t let her settle for 9/10 of a marriage.