You'll have a hard time taking a live-and-let-live attitude about each other, because you'll have such basic and important beliefs that are at odds. Your spiritual views are likely to be completely different, and instead of respecting each other's beliefs, you'll both probably cling even more fiercely to your own as if they're the only acceptable option. So who's right and who's wrong?
That's just the problem -- neither one of you! These are your opinions, after all, and nothing to argue about. Education could become a big issue between you, especially if you've reached different levels of it. And if you plan to travel together, get ready for some major disagreements! If you communicate well and treat each other with respect, this aspect shouldn't be too hard to deal with, but if your communication is already afflicted, expect some battles.