You have to explain to him how he/she deserves better and tell them that life will be so much better if they leave the relationship (if they haven’t) and have them block the person on all social media.
It depends on how the relationship is going, if this relationship is a toxic situation it will definitely effect your health. Some of the symptoms are always stressed, extreme anxiety, mood changes and sleeping problems. To fix this, simply cut off the other person or if possible, try to fix things.
C. By overstimulating the “reward circuit” of the brain
Homeicide would be your answer sorry if I am wrong