Memories that's has no value.

Is really ripped me out when I find one of my girlfriend who has just having a broken relationship and she couldn't accept a new relationship in this short times. I'm not saying she is bad but I'm just saying why are some girls could actually do it? She cherish the past relationship so much and the memories is still very much alive. Does that means those memories are no longer valued to those who engage themselves into a new relationship in a short period? I really can't understand this, aren't them human with feelings? Maybe they are Aliens.