We all make the mistake of getting in over our heads with someone that our friends tell us is clearly psycho or not quite right in the head. It can start out as a challenge when you first start dating such a person and you may find them exciting and fascinating, but quickly the challenge and the excitement turn to the realization that you need to end what you have started because you don't have the patience or the understanding to continue dating someone who is not stable.
The first thing you need to do is get your belongings back. If the less than stable person you have decided to break up with has your things, it makes sense to get back all of your things before the breakup, otherwise you may not see them again. A lot of people, when they are going through a breakup, will ruin the belongings of the other person or they will actually hold the items hostage. You can get your things back subtly, and chances are that they will not even notice.
Next, you want to gather his or her belongings that you have at your home and put them together in a bag or box. When you actually break up with this person you can hand them all of their belongings so you do not have to worry about any tense moments and you can also make a clean break because you have given them everything of theirs back and taken your things in the process.
If you have shared personal information with this person you need to be sure that you change all of it. Think of any passwords or profiles that they may have access to, and be sure that you change all of the log in or personal information so that they cannot access your information and cause trouble for you.
When you break up, do it in a neutral place. In fact, you may find that it is a good idea to break up in a place where a scene is less than likely to be made. Go to a coffee shop, a park, or something of this nature. This will allow you toe tell them that you don't want to see them anymore and hopefully keep things controlled.
Make sure when you breakup that you keep things as distant as possible. Don't give into the temptation to hug or kiss him or her goodbye as this will just give the impression that there is something still there between the two of you, and it may have them continue to pursue you. Make a clean break, no hugs, no kisses, and certainly no break up sex as you are just sending the wrong message.