co-worker drama

So, at my job there is me and one other person who hold the same position. Generally I work on the first floor and he works on the second. Him and I follow the same schedule. We work the same hours, or at least we're suppose to (I'll get into that later). Our boss tells us him and I are "equal". We are both managers. So on and so on.
Between both of our floors, my office is the office with the computer. So he is always coming downstairs to use my computer and eat at MY desk!!!! It drives me crazy!! He always finds a reason to be on my floor. I just want to yell at him, "whats going on upstairs why are you down here in my space?!?!" We have our own floors for a reason!! But like I was saying, hes always downstairs, being nosy, and wanting to talk way too much and not do his job!!
Whenever we have an event that we have to put on, BAM! All of a sudden I cant find him anywhere!! I cant tell you how many times we have planned an event together and I end up setting it up, entertaining and then cleaning up everything. Here we are, supposedly "equal". Where is this guy when I need him? Any other given day I turn around and practically run into him. But when something important is going on or we are being put on the spot....my "equal" is no longer there. 
Also, on days I have class I leave work about 30 minutes early. So on days when I need to leave early he finds it necessary to leave early as well!!! 
I really needed to vent about that!! LOL