This seven page article in pdf format examines ‘cohabiting with children’ verus ‘married with children’ and the long-term consequences. Mentioned in the article is recent research that found that “65 percent of children born to cohabiting [unmarried] parents will see their parents part by age 12, compared to just 24 percent of children born to married parents.” That statistic is startling. Although children can have good lives with parents living in two separate households, it is undeniably stressful for everyone.
If you or someone you care about is struggling in a relationship, please consider counseling. (It's hard for me to write that without feeling like a commercial, but it's true.)