If you decide to live together, yes, there will be problems. If you have kids together, much more so. I have spent ten years on thefor former Christians. I have seen too many heart-rending stories of men and women who met and married while both were devout Christians, and had children. Later on, one or the other deconverted from religion and too often the remaining Christian divorced the atheist. At times, the Christians (either spouse or spouse’s parents) feared the evil influence of the atheist parent on his/her own children for no other reason than their unbelief and did all within their power to keep the children away.
But let’s say everyone accepts everyone with all their foibles and various life philosophies. When it comes time to enrol the children in school, or teach them how the universe came into existence, or the meaning of Christmas, or they grow up having sex outside of marriage, or any issue on which the religious person feels commanded by God to take a stand while you feel driven by your conscience and love of truth to be honest with your own kids….See where this is going?
Kid: Why isn’t Star Wars true but it’s true that Elijah went to heaven in a fiery chariot and horses?
Kid: Why can animals talk on cartoons and in the Bible but Rex never talks to me?(Conversation between Serpent and Woman), (Conversation between Ass and its Owner)
Kid to Atheist Parent: You’re going to hell if you don’t get saved. I know. My Sunday School teacher said so! (Imagine how the kid would feel. I’ve read testimonies about people who experienced this. Kid desperately wants Dad to be saved—and safe—but can’t do a thing about it. It can cause nightmares.)
Those are some of the things I can think of that can cause serious enough problems to break up marriages and families. Yet there are also happy lifelong marriages in which the partners have never agreed on Cosmic Truth and the children made their own decisions when they grew up. I don’t know how they did it; I only know it is possible in some cases. Hopefully some of them will also reply to this question so you can make an informed decision. All the best!