1. Your focus should not be on changing someone else's behaviour. It should be on what you can do no matter what their behaviour. Not let it limit you. If you think you need to change someone else before you can achieve your own success, then you're limiting yourself. Our own habits are our own stumbling blocks. If we wait for someone else to change their habits knowing we stumble, we can never be certain another person has changed and will never move forward.
Never say never.
If someone else has a habit that is harming you, need to move out of harms way. Seek support to help you deal with problem. And focus on what you can do and having the strength to follow through.
In keeping with the law of attraction, You need to work on yourself. If someone is in a relationship with a person who has a detrimental habit, they attracted that person with the detrimental habit. If you don't like their habit you have to stop attracting that, which means you work on yourself not them.
Alex