I think nox is spot on... Once or twice is coincidence, but if it's really happening a lot more than that, then you need to investigate. You are picking Mr Wrong, and doing it over and over. Why? What danger signals are you missing? What do they have in common that other men - the ones that stay faithful to other women, your friends, say - don't have? Are you perhaps actually drawn to men who treat you badly? Does this in any way reflect your parents' relationship? (We all very frequently find ourselves looking for our fathers'/mothers' characteristics, good or bad). You're not necessarily causing the breakup of relationships by doing something wrong, but perhaps the something wrong is your choice of men in the first place?