Being part of a relationship should never be a time when any type of bullying is acceptable, and a person who chooses not to change should be left behind. Many bullies today have learned that they will be held accountable if they engage in physical violence, so they have changed their tactics to get what they want. A person who is experiencing bullying often feels they must justify their choice, and it can be difficult if there is little or no physical evidence to support their claim.
A relationship between two people should fulfill the needs of both of them, but that does not occur when one person is being bullied. They are giving up their right to even have needs, so there is no reason for them to remain. Explaining it to family and friends might be difficult, but the decision to walk away is a good one that needs no justification.
Living with another person to build a future life for both of them is a basic reason for remaining, but there is no future for someone who has a bullying partner. They tend to exist on a day-to-day level, and it leaves them little energy to make or execute plans that will build a good life for them. No matter how emotionally attached they are, they will never be able to reasonably engage their partner in anything that might make their life better.
Walking away without justification due to lack of evidence is a difficult move, but it must be done if the person wants to live a good life. They must take with them the knowledge they have done the right thing, and they have to ignore all those who try to get them to return to their former partner. If they can survive through the initial onslaught of doubt from family and friends, they will be well on their way to a better future.