Listen to your friend without judgement.
There are many reasons why victims stay in violent relationships and various reasons for why they return. Your friend may leave and return to the relationship many times before leaving for good. It takes on average 7 attempts for victims to leave their abusive relationship before leaving for good.
Encourage your friend.
To participate in activities outside of their relationship with family and friends. Abusers tend to isolate their victims as a way to gain power and control over them. Your support is very important, the more your friend feels supported by people who care about them, the easier it will be for them to take the steps necessary to leave their abuser.
Help them develop a safety plan.
Create a code word with your friend that can be used to notify you for help, agree on a safe location your friend can meet you at when they are afraid or in need for help.
When in need get support.
Encourage them to talk to a trusted adult who can provide help and guidance. For instance, that may be a school official like the nurse, a counselor, a teacher or any other adult.
Keep your communication door open.
After the relationship has ended your friend will still need support. They may feel sad or lonely once the relationship is over and still will need time to mourn the loss of the relationship once it's over.