I understand that the OP has already broken up, but I feel I still have to answer this.
I take a similar but slightly different tilt—much more than just what church my child is going to be raised in (which, btw, is a very very grave matter, I acknowledge): I take it as a matter that a husband and wife are called to be united to each other in the flesh—perpetually—as a domestic church. How then can they be a “domestic church” if they are not even united in the same church (religion?). The domestic church exists even if there are no children in it. Catholic marriages are traditionally witnessed before the same altar at which the Holy Eucharist, the sacrament of unity, is offered every Sunday and more. What does that say about the unity of the Catholic church when a Catholic family cannot even receive from the same chalice each Sunday or eat of the same Host? Marriage, according to St. Paul, is an emblem of the marriage of Christ and His Church. In my own opinion (and not that of the Church), a marriage between a Catholic and a non-Catholic is still imperfect as regards this symbolism even absent domestic disputes and headaches. This is NOT to say that these marriages cannot work out, it is just to say that the couple’s calling to be an eschatological reminder to the world of what remains after the grave (the unity of Christ and His Church) cannot entirely be fulfilled (once again, only in my own opinion, as regards the imperfection).
Also, getting back to matter of raising your children, I admit, a more pragmatic concern: what about giving your children every opportunity to grow in faith, such that hopefully he/she will attain to a life of everlasting bliss? For us Catholics, this includes reception of Holy Communion, the making of a Holy Confession throughout your lifespan, and before any of this, the bringing of your child to Holy Baptism. Remember that God gave these things for our benefit. Also, these opportunities for your children include, according to the Catechism, you and your spouse being the first teachers of the faith and morals to your children. What are you going to teach your children if you do not agree on what it is? I know that some of my classmates who had a Catholic and a non-Catholic parent, respectively, were not raised Catholic.
Also, I’m not making a judgment on the OP, but often when a Catholic dates a non-Catholic, it is the Catholic that converts to the non-Catholic church rather than the reverse.I’ll offer that one of the reasons I am still Catholic is that both of my parents agreed to the basic Truth of the Holy Faith. Yes, there have been many disputes over temporal matters, but they agreed on one Faith. One and only one. They may or may not have been able to give a precise theological treatise as to what moment the bread and wine become the Body and Blood of our Savior, but they agreed that there was only one Church founded by Christ. Would there have been a disagreement between the two, I may be something else today—I don’t know, maybe either Eastern Orthodox or Anglican. Their marriage has lasted from the time they got married over 30 years ago to this very day.
Finally to say nothing of the divorce rate in the western world.
These are no slight matters.
Many years,
Paul R. Viola