I'm sure everyone who's ever dated has at one point in time had to deal with a "Destructive Relationship." Before we can figure out how to deal with the situation at hand, one must first figure out how to know some signs of a destructive relationship.
1. If she/he forces you to do things you do not want to do.
2. If she/he takes anger caused by another incident on you.
3. Do you ever feel afraid of the person?
4. Has she/he ever lied to you about something you knew for a fact happened?
These are just a few of the many, many things to look for to spot a destructive relationship. Now that we know how to spot one, whats the best way to deal with it? Theres no one method fits all answer to this dilemma. But the #1 rule to follow with this type of stuff, is to do what makes you happier in the long run. If you have an over possessive significant other who would probably go psychotic if you left them, than you will have to take more drastic steps to end the relationship.
Breakups are hard, but the only way to do it is to sit down and talk. If you are afraid to talk about it alone with the person, in fear of them getting physical, then have a relative go with you. I say relative for one specific reason, say Brianne wants to break up with John but fears John will lose control and maybe harm her. So she brings along her friend Fred, Johns first thought instinctively will be that he is getting replaced by Fred therefore causing more problems than desired.
But what if they beg, and ask for another chance? Then ignore them, chances are at this point you have given them multiple chances and their attempts to fix what was wrong has failed. This is the point of no return and the best option is to leave and give them time to cope with you not being around any more.
A wise man once said, "Only a fool keeps trying the same thing over and over, expecting different results."