Psychopaths are constantly comparing us to others, especially their exes and past sources of supply. It can be quite flattering at first. We're so much better than his last crazy ex. He's never felt like this with anyone else. You're more beautiful than all of the other people he's been with. His sad friends are so jealous of the love you have.

But it becomes much less flattering when you enter the devalue phase. He never had issues like this with his easy-going ex. You're so much needier than anyone he's ever been with. No one has ever had these problems with him except you. He doesn't behave like this with his amazing friends.

Normal, empathetic people do not make such comparisons about the people they love. Sure, in our heads, we might notice: Oh, this person is better at such-and-such. The difference is, we don't keep a public tally for everyone involved to see. When we're truly in love, we don't need to convince ourselves and others that this experience is better than all of our past experiences. Likewise, if we're falling out of love, we don't need to convince ourselves and others that this experience is worse than all of our past experiences.

But a psychopath's mind functions more like that of a bratty child with toys. They do need to convince themselves of all of those things, because they live in a world sheltered by their own impulses, delusions and lies. Now that I have a GI Joe, my Pokemon cards are stupid! This is ridiculous, of course, because the Pokemon cards are still the exact same cards as they were before. It's just that the child has readjusted his reality in order to convince himself that he's made the right decision.

Psychopaths are alarmingly similar. They're constantly assessing us and determining our value as a source of supply, especially our value as compared to other sources (because that's all that really matters, right?). The frightening difference between human beings and toy cards is that a psychopath actually does have the ability to change us, turning us into monsters (see Manufactured Emotions) in order to prove that his new conquest is better.

Psychopaths function on two extremes: obsession and contempt. You need to fit into one of those categories, and he will manipulate you to make that happen (either by idealizing or devaluing). This is why he cannot simply dump someone. He must first devalue, because that means other sources are better by comparison. And during this devalue, it's extremely likely that he's currently idealizing someone else and explaining to them how much better they are than you (just like he did to you and his last "crazy" ex).

Beware of people who make constant comparisons, whether they be positive or negative. You will notice over time that these comparisons are constantly changing, and he will punish you by re-idealizing past sources (even after he's said terrible things about them) in order to remind you of your place in the relationship.

We must understand that a healthy individual does not see love this way. Real love is a bond of mutual respect, passion and kindness. No one should be giving you frequent status updates about where you stand in comparison to others. No one should be re-arranging you in their mind like some sort of collection. No one should be declaring why you're any better or worse than anyone else. Because you're not. You're you. And you deserve to be treated as an individual, not as a child's toy.

Source: http://psychopathfree.com/showthread.php?354-Psychopathic-Comparisons