I'm being haunted and I have no idea what to do

The supposed spirits of the dead are demon spirits.

contact a priest or exorcist, or you can demand that the ghost leave your house.

Science says hauntings are not real,it could be something else

Call ghost hunters

Oh my god that is SCARY!!! I am so sorry :-(

If the building that you are living in is a new addition to the area or if rennovations have been done to it if it's older(or if you have made changes to the apartment yourself), this may have caused a disturbance in an energy that was peacefully resting. You say that he did not react much to your presence until you confronted him. Be careful about this. You may cause it to become more angry and lash out in worse ways than eating your food. :/ For the most part when things like this happen, it's just a lost soul who's trying to figure out why somebody else is in HIS house. Remember, he was there before you, so he's more afraid than you are. Easy fix is to have a preacher come to the aparment and do a house clensing. If you prefer not to use a religious approach, you can also wait until the late hours of the night, (usually between 12-4am) turn off all the lights, and CALMLY, attempt to communicate with it. Ask it to make soft noises in response to your questions, and make sure to let him know you are here to HELP, not harm. Also, if he is still hanging around in our demetion, he may not know that it is his time to go, so reinforce the fact that this is now YOUR house, and that you would like him to move on. Spirits are forms of energy that are usually easily intimidated. If he still refuses to leave, you may also try a very firm, commanding tone to tell it to leave, telling it that it is YOUR home and he is no longer allowed to be there because he is interfering with your life. If you do want to communicate with it yourself instead of a house clensing, keep in mind that it may take a few nights for it to come around and see that you are friend, not foe. Remember, his spirit has been around mich longer than you, and things back in his day were way different than they are now. So he's just as lost and confused as you may be. Hope this helps.
PS: There's a group called Paranormal State that you can contact if things get out of hand and you really need help. They're a great group.