I just don't get it

Why do some women think they're "in love" with guys who treat them like crap? You hear about it all the time. See it on talk shows, or on COPS. Read about it in the paper. And probably know one or two personally. My friend Liz is a perfect example. She's a truly beautifull young woman . . . incredibly pretty, usually smiling, smart as a whip, caring, an absolute sweetheart. But her boyfriend's a jerk. She's convinced that she's completely and utterly in love with him, and that he loves her too. But I don't understand how she can believe that. He's stated outright (to her and others) that they should both continue seeing other people--supposedly so they'll appreciate each other more [gag!]. I've seen him publicly bring her to tears, and then still not let up and keep arguing. And usually the argument in question comes about because of his own selfishness. When she's feeling down, or ill, he's nowhere to be found--off having fun with his friends. I and others have talked with her about things. But she's just convinced that we're all wrong and simply "don't understand" his love for her. I just hope she comes to her senses before making a huge mistake like letting him get her pregnant or something. But in the meantime, I just don't understand why she puts up with him.