Plenty of people, even most Christians having not read the Bible, have good morals. Atheists, Hindus, etc. all have a sense of morality.
This topic of Morality is a huge topic. So, just going to make a couple of real quick points, that's all.
There Objective and Subjective morals.
“Objective” means “independent of people’s (including one’s own) opinion.” “Subjective” means “just a matter of personal opinion.” If we do have objective moral duties, then in the various circumstances in which we find ourselves we are obligated or forbidden to do various actions, regardless of what we think.
Atheism and those others that do not believe in God, typically are in the Subjective moral ranks.
As it says above, it's just a matter of personal opinion.
Christianity typically are in the Objective moral ranks. We ought to do and ought not to do things, despite what we think or feel. It isn't about us, It's about God and His Word, which we have faith in and believe.
So, marrying or dating an Atheist, could be problematic, because of the moral difference of thought and actions.
This is why the Bible tells us to not be unequally yoked. Also why as Children of God, we aren't to be part of the World. We are to be a peculiar people. Separated from the World.
And no one is good, not one of us.
Then why does it seem like atheist marriages last longer than Christian ones?
Where did you get this information from?
I've been to the cdc.gov where they keep very detail records of marriage stats. Cannot locate anything on the different beliefs. Not saying they are not there. I just could not find anything. Just want to update any stats that I may have that are incorrect.