I was a very lukewarm Christian as a youth i.e. I said I believed in God, but it didn't really impact my life at all. However, after getting married and having children I also became very serious about my religion after a series of events.
Luckily, over time, my husband also found God (not through pressure, but from openness and honestly and his own exploration) and now we are extremely happy.
Biblically, if one person finds God and the other doesn't, there's no need to divorce over it. Personally, I would have had a huge struggle if my husband was an atheist as I would not be happy to raise my children as atheists or with this idea of God as "something some people believe". To me it is the most important thing to raise them as Christians.
It would also be really difficult to not be able to share my religion with my husband. Atheists are often very dismissive and mocking of Christianity. I don't know how I'd have coped if he'd have been like that.
As a Christian, I wouldn't have divorced my husband, as obviously this isn't encouraged within Christianity. But I will admit it would have been difficult at times. I suppose it depends on the level of commitment of the Christian, and the openmindedness of the non-Christian about religion.
If you're married, it's always worth fighting for.
If I was unmarried and didn't have children and I found God while my partner remained an atheist, I would end the relationship.