I think it is some kind of universal law of dating, that you must have at least one psycho ex before settling down...
My psycho ex was the result of a blind date. Long story short - after about 4 months of dating, he abruptly decided that he couldn't be with someone of a different religion, and would I mind converting?
My husband's psycho ex was a worse nightmare. She met him during rush her freshman year, and she actually chose her dorm and entry because he lived there. She was very needy and clingy. They dated for several months before he realized she was nothing but bad news, and he ended the relationship.
This chick also really wanted to be in my sorority - but it was plain, even just from the brief conversations we had during rush, that she wanted to join for all the wrong reasons - she wanted Greek letters and the "instant popularity" she thought that would bring, and she wanted sisters to lean on for support, but didn't want to give that support in turn.
To this day she bears a grudge against me, because she thinks I kept her out of my sorority and because she thinks I stole her boyfriend (in her twisted mind... my husband and I started dating well over a year after they had broken up).