With my first girlfriend, I kind of moved on when I went away to college, two years ahead of her. I behaved like a real shit, just sleeping with whomever I wanted and taking it for granted that my girlfriend back home would always be there. Finally, she broke up with me. After some time, I realized what I'd done and felt HORRIBLE about it. I tried to win her back, but there was just no way. I was heartbroken about her for years.
My next serious girlfriend cheated on me and I felt pretty heartbroken about that. The feeling didn't last, fortunately. She decided she wanted me back (after getting dumped by the guy she cheated on me with). I accepted the "friends with benefits" sex, and although I'm not proud of it, I did enjoy seeing HER heartbreak.
My third serious girlfriend and I were almost
perfect for each other, except that she really wanted to have kids, and to have them soon (biological clock, she was several years older) and I really didn't want to have kids. We split, but did friends with benefits for a couple of years. The whole time, I was hoping she'd give up on the kids so we could be together, but it didn't happen. Although I knew it was coming, when she did meet someone else, I was deeply hurt. That feeling only went away when I met the woman who's now my wife, several years later.
Of course, I've felt terrible about people I loved who died (not to mention pets), as well as other losses. If you dare to live and love, you'll experience heartbreak. But it's worth it, in my opinion.