You've finally met someone who seems to be perfect. The only problem is that she can't stop talking about her ex-boyfriend: How handsome he was, how perfect in every way, and how he tore her heart into little pieces. You know the color of his hair, the exact shade of his eyes, and what made him laugh. How are you supposed to start a relationship with a girl who still hasn't finished her last one?
It's understandable that we tend to hold on to the relationships that were most special to us. As time passes, the ex in question gets put on a pedestal. All of his or her transgressions are forgiven and forgotten, until only the good memories remain -- even if the relationship itself was far from perfect.
If you're the new girl or guy, it can be hard to live up to an ex's idyllic standards. Whether you stick it out and hope that the person you're dating will eventually move on and get more into you depends on how invested you are in the relationship. You can make an ultimatum -- "It's her or me" -- but only if you're prepared to walk out if the answer is "her."