I know two couples, both started dating young at the ages 15/16. I'm not aware of the details - the breakups occurred so long ago - but I'll summarize.
One of the couples had a baby at 17 and split up for a few months a year or two later - they weren't apart for too long but, during that time, it was bad. The girl even sued the guy over something trivial and they went to court. She slapped him and the guy tried to press assault charges on her. It was crazy. Now, though, they've been back together for about eight years and have another child.
The other couple split up for six months during their early twenties. I don't know the details - but they're together now and very happy. They're getting married in 2014 and, in all, have been together for eleven years.
Also, Frida Kahlo and Diego Rivera had a notoriously rocky relationship. They separated for periods of time but eventually made up. However, they eventually divorced after a few affairs - Diego cheated on Frida with her younger sister. They remarried over a year later and stayed together until Frida's death. There was a quote by Diego, I can't remember quite how it goes, but he said that Frida's death was the most tragic experience in his life and he never knew how much she meant to him until she was gone. Both of them, during their lives together, always had a very strong love/hate relationship. Their quotes about each other range from pure hatred to undying love.