Break up after baby

I just got to thinking today about how many couples break up after a baby (or two, or three). So many people I know who were together for years, even high school sweet hearts, have a baby and it seems like a couple years pass and they are broke up or divorced! I have a two month old so I know babies can definitely add stress to a relationship, but what's some advice you ladies have for making a relationship last? I'd also be interested to hear from women who are no longer with their SO after baby and what caused the break up