adjective 1.influencing or attempting to influence the behavior or emotions of others for one’s ownpurposes: a manipulative boss.
We have all met someone who is like this... Who thinks they can toy with our emotions or the emotions of someone we care about.
So expect them in your writing. Although it is hard for someone who does not work like this on a daily basis and get in the head of this character, it isn't any harder than getting in the head of a murderer.
Just because someone ticks in a way that is nothing like how you tick doesn't mean you can't see things from their angle.
Manipulative people try to control those weaker than themselves.
So they either attack those with low self esteem, children or those who are weak because of illness or other physical variable. They try to worm their way into the weak persons psyche by 'taking care' of them. What they are really doing is looking at the end game. They are little better than emotional con artists- They see a crack, they work their way in and...
Then they take control.
You can have a bit of fun if you make your other characters play along and not see it at first. Some of the best suspense is written with this character at the core... Everyone is blind to the bad... and then it comes up and bites them in the ass.
Breaking the cycle.
The easiest way to break the cycle is to end the abuse.
Because manipulating others IS a form of abuse. End the cycle, end the abuse.
Just some ideas. Happy Writing!