Well, if two people are committed to Christ that means they have crucified their flesh, and are living selflessly for the other. They've both made the decision to uphold the word of God and walk in His ways. A marriage like this should flourish, not end up broken.
Unfortunately, it doesn't end up that way very often. Not very often at all--one glance at the titles of threads in the Family Forum will give you and idea how often this seems to occur. God's Word is absolute, but the realities of life in a fallen world are, most often, vastly different. I often think many Christians concentrate more on the ideal than on what really happens in life and how to get through it.
I agree with some of the other posters... I can be very hard-headed and prideful... If it were someone I thought I was really crazy head-over-heels in love with, even if I thought someone else would be better for him, I have to admit that my first thought would be, "Whoever he wants or needs, I can make myself (or pray to God that I become) that person."
Which, of course, is probably not the right line of thinking.