Here are some key points from the article which should reinforce your confidence in your approach:
Emotional Signs of abuse:
Low self-esteem
Changes in sleeping or eating patterns
Anxious or on edge
Substance abuse
Symptoms of depression
Loss of interest in once enjoyed activities and hobbies
Behavioral Signs of abuse:
Becoming withdrawn or distant
Canceling appointments or meetings at the last minute
Being late often
Excessive privacy concerning their personal life
Isolating themselves from friends and family
What you should do:
Validate the Victim's Feelings
It's not unusual for victims to express conflicting feelings about their partner and their situation. These feelings can range from:
Guilt and anger
Hope and despair
Love and fear
If you want to help, it is important that you validate their feelings by letting them know that having these conflicting thoughts is normal.But it is also important that you confirm that is not okay, and it isn't normal to live in fear of being emotionally or physically attacked.
Don't...
Bash the abuser.
Focus on the behavior, not the personality.
Blame the victim. That's what the abuser does.
Underestimate the potential danger for the victim and yourself.
Promise any help that you can't follow through with.
Give conditional support.
Do anything that might provoke the abuser.
Pressure the victim.
Give up. If they are not willing to open up at first, be patient.
Do anything to make it more difficult for the victim.
This advice is for independent adults so it’s v hard in your situation - but equally as delicate - seems that it’s a v fine balance of keeping doors open, diplomatically pointing out generic abuse behaviors, building their confidence so that they can see it’s wrong, not normal, that they don’t deserve this and have agency to either change the dynamics/balance of power or get out.
I am concerned that all his normal “touch points” - with emotionally healthy people - work, sport, friends, family are being eroded bit by bit and he is under stress at school.