Breaking a trust .. is the worse thing in ANY relationship (parent.child) (husband/wife)(boyfriend/girlfriend)(friend/friend) ... Trust is the glue that holds relationships together. If you undermine the bond of trust .. you have nothing.
Cheating. That will either let the boy or girl feel insecure that they are not good enough. Cheating really boosts down ones self esteem. Instead of cheating, he or she should instead tell the person face to face. The second thing might be an abusive/ forceful relationship. That is initially one of the worst things in the relationship. Hoped this helped! :)
Breaking someone's trust, cheating, lying, hiding something, lying about your age,Using that person for money, forcing to be in a relation ship,arguing, rude to that specific person,abusing,threatening hope that helped!