Inner Conflict

i'm having somewhat of an inner way going on within me. the matter concerns my job... I work at a retail computer store and, well, I’ve always been somewhat unhappy there. I have the mentality that things will get better with time. the reality to that is that they have gotten worse. let me chronologically break this down so you understand.
I started working at this job on July 5th, 2005. I was replacing another worker in a team of two. a month later after I started, I was left alone to do a job I was poorly prepared to do. I was the only one to do it, so I did it. between august and January, being in charge of my team, I’ve trained about 10 replacements. some lasted a week; couple of days, a day, and even down to a few hours (left and never came back from lunch break)! I finally found a great couple but both left in January for school.
from Jan-May, i'm in school and don’t want to leave my bi-polar (possibly, who knows?), jack a$$, uncaring, inconsiderate, insensitive boss hanging. I stay and work a half shift from 7am-11am. Still the head of my team, I take on more employees that come and go and one really good and outstanding worker. situations arise in the beginning of may which cause him temporarily to be out of work, which leaves just me!
around mid march I ask my general manager if he has a manager position available for me. the reply is no. he stated that when the merchandising manager opens that I’d get it. come middle of may, without my knowledge, a sales girl was promoted to a position over me. her title, merchandising manager! I was pissed. beyond pissed. I storm into the warehouse flying off the handle cussin' up a storm. and I don’t cuss, I bleep on most occasions. so this airhead comes on to the scene with like 2 months experience of selling stuff and gets promoted over my upcoming year experience. the worst of all of it, THEY WANTED ME TO TRAIN HER!!!
this girl thinks that her ish don’t stink. she's bossing everybody around and making enemies very very very fast. her car was keyed (a classic) and nobody likes her at the job. she's making everybody's life a nightmare. now, i'm being placed with a full day's work to do in 3 1/2 to 4 hours! bull straight bull. and I know it’s the result of the new boss's moaning and groanings to the GM. I really want to comeback full time but they make me want to quit.
I have been looking for another job for quite some time. I need a specific type of job that will allow me to go to school as well as work. not easy given the school hours. here is the dilemma. I really want to leave but have not felt led to leave. for the summer i'm able to work fulltime. at the same time I can leave my job and look for what I’ve always wanted, a job in the kitchen. if I choose to leave I’d be in the group that is giving their two-weeks notice in tomorrow. yes I said group! if I stay, i'm going to be miserable because the slack is going to fall on the rest of the workers. if I leave I can start fresh at another job doing what I should've been doing in the first place, but starting at the bottom and working my way up again :-(

I do and don't want to leave my job, what should I do?