Say there could be a reason, like they've known each other like forever, or their parents/friends are friends and so on. Say they talk a little almost every day, hang out maybe once a week/two weeks. Would you be ok with that?
Most Helpful Guy
It will always be difficult, but trust is a biggie in a relationship. I would be uncomfortable with it, but maybe if I get to know the person better, I may understand why she's still friends with her ex or something and perhaps even get along with him.1
Most Helpful Girl
Tbh I'd probably become friends with their ex so he/she would feel guilty cheating on me. That way I've secured that fear and made a new friend!1