Most people who "break someone's heart" didn't mean to. They thought they were in love but they weren't. Or thought they were ready for to get serious, get married, start a family, but weren't and had to get out. Two people loving each other permanently is much rarer than we realize. It seems to be happening all the time, but most of the time one person loves, and the other doesn't. That's why it's so special when the love is mutual and real.
i think once you have mutually fallen in love with someone. you set high standards. with love comes trust. when we love someone we hope and trust they wont be the ones to hurt you. inevitably broken hearts and dishonesty are all too common.