Yes, I quit my job.

So I have worked at BBW for over a year. I recently got a promotion and became a member of management. It was a fun place to work and the employee discount and pay was pretty good. Most of the people I worked with were fun to be with. with the exception of one. Nicholas, the co-manager has been a pain to work with from the beginning. No one wanted to work with him and he had complaints coming out of his ears from both customers and associates. Needless to say he and I never got along, but I tried to keep it between he and I behind closed doors. I found out yesterday that he just got his final write up.
I have never been written up or had even one verbal warning or complaint, except by Nicholas, apparently. I went into work yesterday just as Nicholas, my Manager and the District Manager were coming out of the back room. They had a meeting. Now it was my turn. They said that it was apparent that Nicholas and I did not get along and I was not happy there (I wasn't) and I had to resign effective the next day or they were going to fire me making me not rehire-able. Therefore a whole year of job experience down the drain. Not to mention all of the training I got when I was promoted.
I am angry and confused. I still can't figure it out. He has been walking on a thin line for a very long time. In fact When I was promoted I was instructed to keep him in order because he was close to loosing his job then. I am over it now and I really don't care but why was I the one forced to quit? Why not him? I have a`perfect record and wonderful reviews.
Whatever, I am done venting now. Thanks for listening.