It’s a fascinating topic to study, but not to live in it, in real life!
There are a host of reasons why this pattern of behaviour persists;
* Early life conditioning/experiences
* Previous unhealthy relationship that has destroyed your self-esteem
* Feeling emotionally dependent
* Becoming financially dependent
* Lacking in self confidence due to any of the above
The list is endless really and thousands of people can often relay a story that is unique to them.
The method of breaking the cycle is an interesting and healthy one. Essentially, it involves an assessment of your history, maintenance factors and your desire to change.
The length of the process to achieve change obviously depends on the circumstances, if they appear to be long-standing then they can take time, compared to a situation that is fairly current.