Hi notthisagain.

First order of business…If he has a key to your apartment, arrange to have a deadlock installed asap. Also he will undoubtedly insist on a reason as to why you don't want to be with him anymore..Try to be kind but firm, without citing his faults, but your own goals.
As in…'I dont want to be in a relationship right now' or ' I want to focus on my study/work'.

It is important to keep all animosity to a minimum…as he could very well become hostile. Ensure that you let your neighbours and family know that you have broken off with this man, so if he starts to create problems for you there is support around you.

I hope that you can move on quickly from this, and just remember that you deserve to feel safe & be happy.